From c60e8f3d295e3d2d045711021a1f0dfe8e1dcb27 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marco=20A=2E=20Guti=C3=A9rrez?= <marco@openrobotics.org>
Date: Fri, 18 Jun 2021 02:37:51 +0800
Subject: [PATCH 1/8] Making PrintValues() and ToString() able to not print
 default elements (#575)

Now PrintValues() and ToString() will not output the elements that were added by default during parsing. There's also the option to call them with a boolean flag that will allow the caller to decide weather they want defaults in the output or not.

Signed-off-by: Marco A. Gutierrez <marco@openrobotics.org>

Co-authored-by: Addisu Z. Taddese <addisu@openrobotics.org>
---
 include/sdf/Element.hh               |  28 +++++++
 src/Element.cc                       | 111 +++++++++++++++++++--------
 src/Element_TEST.cc                  |  70 ++++++++++++++++-
 test/integration/default_elements.cc | 104 ++++++++++++++++++++++++-
 test/sdf/empty_road_sph_coords.sdf   |   2 +-
 5 files changed, 275 insertions(+), 40 deletions(-)

diff --git a/include/sdf/Element.hh b/include/sdf/Element.hh
index 6064abf3a..798f7828e 100644
--- a/include/sdf/Element.hh
+++ b/include/sdf/Element.hh
@@ -149,6 +149,14 @@ namespace sdf
     /// \param[in] _prefix String value to prefix to the output.
     public: void PrintValues(std::string _prefix) const;
 
+    /// \brief Output Element's values to stdout.
+    /// \param[in] _prefix String value to prefix to the output.
+    /// \param[in] _includeDefaultElements flag to print default elements.
+    /// \param[in] _includeDefaultAttributes flag to print default attributes.
+    public: void PrintValues(const std::string &_prefix,
+                             bool _includeDefaultElements,
+                             bool _includeDefaultAttributes) const;
+
     /// \brief Helper function for SDF::PrintDoc
     ///
     /// This generates the SDF html documentation.
@@ -171,6 +179,18 @@ namespace sdf
     /// \return The string representation.
     public: std::string ToString(const std::string &_prefix) const;
 
+    /// \brief Convert the element values to a string representation.
+    /// Current behavior of ToString(const std::string &_prefix) can be
+    /// achieved by calling this function with _includeDefaultElements=true
+    /// and _includeDefaultAttributes=false
+    /// \param[in] _prefix String value to prefix to the output.
+    /// \param[in] _includeDefaultElements flag to include default elements.
+    /// \param[in] _includeDefaultAttributes flag to include default attributes.
+    /// \return The string representation.
+    public: std::string ToString(const std::string &_prefix,
+                                 bool _includeDefaultElements,
+                                 bool _includeDefaultAttributes) const;
+
     /// \brief Add an attribute value.
     /// \param[in] _key Key value.
     /// \param[in] _type Type of data the attribute will hold.
@@ -422,14 +442,22 @@ namespace sdf
 
     /// \brief Generate a string (XML) representation of this object.
     /// \param[in] _prefix arbitrary prefix to put on the string.
+    /// \param[in] _includeDefaultElements flag to include default elements.
+    /// \param[in] _includeDefaultAttributes flag to include default attributes.
     /// \param[out] _out the std::ostreamstream to write output to.
     private: void ToString(const std::string &_prefix,
+                           bool _includeDefaultElements,
+                           bool _includeDefaultAttributes,
                            std::ostringstream &_out) const;
 
     /// \brief Generate a string (XML) representation of this object.
     /// \param[in] _prefix arbitrary prefix to put on the string.
+    /// \param[in] _includeDefaultElements flag to include default elements.
+    /// \param[in] _includeDefaultAttributes flag to include default attributes.
     /// \param[out] _out the std::ostreamstream to write output to.
     private: void PrintValuesImpl(const std::string &_prefix,
+                                  bool _includeDefaultElements,
+                                  bool _includeDefaultAttributes,
                                   std::ostringstream &_out) const;
 
     /// \brief Create a new Param object and return it.
diff --git a/src/Element.cc b/src/Element.cc
index 7df8928df..4f3326215 100644
--- a/src/Element.cc
+++ b/src/Element.cc
@@ -442,47 +442,59 @@ void Element::PrintDocLeftPane(std::string &_html, int _spacing,
 }
 
 void Element::PrintValuesImpl(const std::string &_prefix,
+                              bool _includeDefaultElements,
+                              bool _includeDefaultAttributes,
                               std::ostringstream &_out) const
 {
-  _out << _prefix << "<" << this->dataPtr->name;
-
-  Param_V::const_iterator aiter;
-  for (aiter = this->dataPtr->attributes.begin();
-       aiter != this->dataPtr->attributes.end(); ++aiter)
+  if (this->GetExplicitlySetInFile() || _includeDefaultElements)
   {
-    // Only print attribute values if they were set
-    // TODO(anyone): GetRequired is added here to support up-conversions where a
-    // new required attribute with a default value is added. We would have
-    // better separation of concerns if the conversion process set the required
-    // attributes with their default values.
-    if ((*aiter)->GetSet() || (*aiter)->GetRequired())
-    {
-      _out << " " << (*aiter)->GetKey() << "='"
-           << (*aiter)->GetAsString() << "'";
-    }
-  }
+    _out << _prefix << "<" << this->dataPtr->name;
 
-  if (this->dataPtr->elements.size() > 0)
-  {
-    _out << ">\n";
-    ElementPtr_V::const_iterator eiter;
-    for (eiter = this->dataPtr->elements.begin();
-         eiter != this->dataPtr->elements.end(); ++eiter)
+    Param_V::const_iterator aiter;
+    for (aiter = this->dataPtr->attributes.begin();
+         aiter != this->dataPtr->attributes.end(); ++aiter)
     {
-      (*eiter)->ToString(_prefix + "  ", _out);
+      // Only print attribute values if they were set
+      // TODO(anyone): GetRequired is added here to support up-conversions where
+      // a new required attribute with a default value is added. We would have
+      // better separation of concerns if the conversion process set the
+      // required attributes with their default values.
+      if ((*aiter)->GetSet() || (*aiter)->GetRequired() ||
+          _includeDefaultAttributes)
+      {
+        _out << " " << (*aiter)->GetKey() << "='"
+             << (*aiter)->GetAsString() << "'";
+      }
     }
-    _out << _prefix << "</" << this->dataPtr->name << ">\n";
-  }
-  else
-  {
-    if (this->dataPtr->value)
+
+    if (this->dataPtr->elements.size() > 0)
     {
-      _out << ">" << this->dataPtr->value->GetAsString()
-           << "</" << this->dataPtr->name << ">\n";
+      _out << ">\n";
+      ElementPtr_V::const_iterator eiter;
+      for (eiter = this->dataPtr->elements.begin();
+           eiter != this->dataPtr->elements.end(); ++eiter)
+      {
+        if ((*eiter)->GetExplicitlySetInFile() || _includeDefaultElements)
+        {
+          (*eiter)->ToString(_prefix + "  ",
+                             _includeDefaultElements,
+                             _includeDefaultAttributes,
+                             _out);
+        }
+      }
+      _out << _prefix << "</" << this->dataPtr->name << ">\n";
     }
     else
     {
-      _out << "/>\n";
+      if (this->dataPtr->value)
+      {
+        _out << ">" << this->dataPtr->value->GetAsString()
+             << "</" << this->dataPtr->name << ">\n";
+      }
+      else
+      {
+        _out << "/>\n";
+      }
     }
   }
 }
@@ -491,7 +503,20 @@ void Element::PrintValuesImpl(const std::string &_prefix,
 void Element::PrintValues(std::string _prefix) const
 {
   std::ostringstream ss;
-  PrintValuesImpl(_prefix, ss);
+  PrintValuesImpl(_prefix, true, false, ss);
+  std::cout << ss.str();
+}
+
+/////////////////////////////////////////////////
+void Element::PrintValues(const std::string &_prefix,
+                          bool _includeDefaultElements,
+                          bool _includeDefaultAttributes) const
+{
+  std::ostringstream ss;
+  PrintValuesImpl(_prefix,
+                  _includeDefaultElements,
+                  _includeDefaultAttributes,
+                  ss);
   std::cout << ss.str();
 }
 
@@ -499,17 +524,35 @@ void Element::PrintValues(std::string _prefix) const
 std::string Element::ToString(const std::string &_prefix) const
 {
   std::ostringstream out;
-  this->ToString(_prefix, out);
+  this->ToString(_prefix, true, false, out);
+  return out.str();
+}
+
+/////////////////////////////////////////////////
+std::string Element::ToString(const std::string &_prefix,
+                              bool _includeDefaultElements,
+                              bool _includeDefaultAttributes) const
+{
+  std::ostringstream out;
+  this->ToString(_prefix,
+                 _includeDefaultElements,
+                 _includeDefaultAttributes,
+                 out);
   return out.str();
 }
 
 /////////////////////////////////////////////////
 void Element::ToString(const std::string &_prefix,
+                       bool _includeDefaultElements,
+                       bool _includeDefaultAttributes,
                        std::ostringstream &_out) const
 {
   if (this->dataPtr->includeFilename.empty())
   {
-    PrintValuesImpl(_prefix, _out);
+    PrintValuesImpl(_prefix,
+                    _includeDefaultElements,
+                    _includeDefaultAttributes,
+                    _out);
   }
   else
   {
diff --git a/src/Element_TEST.cc b/src/Element_TEST.cc
index ec7897a11..046843004 100644
--- a/src/Element_TEST.cc
+++ b/src/Element_TEST.cc
@@ -540,7 +540,6 @@ TEST(Element, ToStringValue)
             "myprefix< test='foo'>val</>\n");
 }
 
-
 /////////////////////////////////////////////////
 TEST(Element, ToStringClonedElement)
 {
@@ -575,6 +574,75 @@ TEST(Element, ToStringInclude)
   ASSERT_EQ(stringval, "myprefix<include filename='foo.txt'/>\n");
 }
 
+/////////////////////////////////////////////////
+TEST(Element, ToStringDefaultElements)
+{
+  sdf::ElementPtr parent = std::make_shared<sdf::Element>();
+  parent->SetName("parent");
+  sdf::ElementPtr elem = std::make_shared<sdf::Element>();
+  elem->SetName("elem");
+  elem->SetParent(parent);
+  parent->InsertElement(elem);
+  sdf::ElementPtr elem2 = std::make_shared<sdf::Element>();
+  elem2->SetName("elem2");
+  elem2->SetParent(parent);
+  parent->InsertElement(elem2);
+
+  std::ostringstream stream;
+  stream
+    << "<parent>\n"
+    << "  <elem/>\n"
+    << "  <elem2/>\n"
+    << "</parent>\n";
+
+  EXPECT_EQ(parent->ToString("", false, false), stream.str());
+  EXPECT_EQ(parent->ToString(""), stream.str());
+  EXPECT_EQ(parent->ToString("", true, false), stream.str());
+
+  elem->SetExplicitlySetInFile(false);
+
+  std::ostringstream stream2;
+  stream2
+    << "<parent>\n"
+    << "  <elem2/>\n"
+    << "</parent>\n";
+
+  EXPECT_EQ(parent->ToString("", false, false), stream2.str());
+  EXPECT_EQ(parent->ToString(""), stream.str());
+  EXPECT_EQ(parent->ToString("", true, false), stream.str());
+
+  parent->SetExplicitlySetInFile(false);
+
+  EXPECT_EQ(parent->ToString("", false, false), "");
+  EXPECT_EQ(parent->ToString(""), stream.str());
+  EXPECT_EQ(parent->ToString("", true, false), stream.str());
+}
+
+/////////////////////////////////////////////////
+TEST(Element, ToStringDefaultAttributes)
+{
+  sdf::ElementPtr element = std::make_shared<sdf::Element>();
+  element->SetName("foo");
+  element->AddAttribute("test", "string", "foo", false, "foo description");
+  element->AddAttribute("test2", "string", "bar", true, "bar description");
+
+  EXPECT_EQ(element->ToString(""), element->ToString("", true, false));
+  EXPECT_EQ(element->ToString(""), element->ToString("", false, false));
+
+  std::ostringstream stream;
+  stream << "<foo test2='bar'/>\n";
+
+  EXPECT_EQ(element->ToString(""), stream.str());
+  EXPECT_EQ(element->ToString("", true, false), stream.str());
+  EXPECT_EQ(element->ToString("", false, false), stream.str());
+
+  std::ostringstream stream2;
+  stream2 << "<foo test='foo' test2='bar'/>\n";
+
+  EXPECT_EQ(element->ToString("", true, true), stream2.str());
+  EXPECT_EQ(element->ToString("", false, true), stream2.str());
+}
+
 /////////////////////////////////////////////////
 TEST(Element, DocLeftPane)
 {
diff --git a/test/integration/default_elements.cc b/test/integration/default_elements.cc
index e8dcfbac1..970e26db4 100644
--- a/test/integration/default_elements.cc
+++ b/test/integration/default_elements.cc
@@ -31,12 +31,12 @@
 //////////////////////////////////////////////////
 TEST(ExplicitlySetInFile, EmptyRoadSphCoords)
 {
-  const std::string test_file =
+  const std::string testFile =
     sdf::filesystem::append(PROJECT_SOURCE_PATH, "test", "sdf",
         "empty_road_sph_coords.sdf");
 
   sdf::Root root;
-  sdf::Errors errors = root.Load(test_file);
+  sdf::Errors errors = root.Load(testFile);
   EXPECT_TRUE(errors.empty());
 
   sdf::ElementPtr rootPtr = root.Element();
@@ -109,12 +109,12 @@ TEST(ExplicitlySetInFile, EmptyRoadSphCoords)
 //////////////////////////////////////////////////
 TEST(ExplicitlySetInFile, EmptyAxis)
 {
-  const std::string test_file =
+  const std::string testFile =
     sdf::filesystem::append(PROJECT_SOURCE_PATH, "test", "sdf",
         "empty_axis.sdf");
 
   sdf::Root root;
-  sdf::Errors errors = root.Load(test_file);
+  sdf::Errors errors = root.Load(testFile);
   EXPECT_TRUE(errors.empty());
 
   sdf::ElementPtr rootPtr = root.Element();
@@ -153,3 +153,99 @@ TEST(ExplicitlySetInFile, EmptyAxis)
   sdf::ElementPtr upperLimitPtr = lowerLimitPtr->GetNextElement();
   EXPECT_FALSE(upperLimitPtr->GetExplicitlySetInFile());
 }
+
+//////////////////////////////////////////////////
+TEST(ExplicitlySetInFile, ToString)
+{
+  const std::string testFile =
+    sdf::filesystem::append(PROJECT_SOURCE_PATH, "test", "sdf",
+        "empty_road_sph_coords.sdf");
+
+  sdf::Root root;
+  sdf::Errors errors = root.Load(testFile);
+  EXPECT_TRUE(errors.empty());
+
+  EXPECT_EQ(root.Element()->ToString(""),
+            root.Element()->ToString("", true, false));
+
+  std::ostringstream stream;
+  std::string version = "1.7";
+  stream
+    << "<sdf version='" << version << "'>\n"
+    << "  <world name='default'>\n"
+    << "    <road name='empty_road'>\n"
+    << "    </road>\n"
+    << "    <spherical_coordinates>\n"
+    << "    </spherical_coordinates>\n"
+    << "  </world>\n"
+    << "</sdf>\n";
+
+  EXPECT_EQ(root.Element()->ToString("", false, false), stream.str());
+
+  stream.str(std::string());
+  stream
+    << "<sdf version='" << version << "'>\n"
+    << "  <world name='default'>\n"
+    << "    <road name='empty_road'>\n"
+    << "      <width>1</width>\n"
+    << "      <point>0 0 0</point>\n"
+    << "    </road>\n"
+    << "    <spherical_coordinates>\n"
+    << "      <surface_model>EARTH_WGS84</surface_model>\n"
+    << "      <latitude_deg>0</latitude_deg>\n"
+    << "      <longitude_deg>0</longitude_deg>\n"
+    << "      <elevation>0</elevation>\n"
+    << "      <heading_deg>0</heading_deg>\n"
+    << "    </spherical_coordinates>\n"
+    << "    <gravity>0 0 -9.8</gravity>\n"
+    << "    <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>\n"
+    << "    <atmosphere type='adiabatic'/>\n"
+    << "    <physics type='ode'>\n"
+    << "      <max_step_size>0.001</max_step_size>\n"
+    << "      <real_time_factor>1</real_time_factor>\n"
+    << "      <real_time_update_rate>1000</real_time_update_rate>\n"
+    << "    </physics>\n"
+    << "    <scene>\n"
+    << "      <ambient>0.4 0.4 0.4 1</ambient>\n"
+    << "      <background>0.7 0.7 0.7 1</background>\n"
+    << "      <shadows>1</shadows>\n"
+    << "    </scene>\n"
+    << "  </world>\n"
+    << "</sdf>\n";
+
+  EXPECT_EQ(root.Element()->ToString(""), stream.str());
+  EXPECT_EQ(root.Element()->ToString("", true, false), stream.str());
+
+  stream.str(std::string());
+  stream
+    << "<sdf version='" << version << "'>\n"
+    << "  <world name='default'>\n"
+    << "    <road name='empty_road'>\n"
+    << "      <width>1</width>\n"
+    << "      <point>0 0 0</point>\n"
+    << "    </road>\n"
+    << "    <spherical_coordinates>\n"
+    << "      <surface_model>EARTH_WGS84</surface_model>\n"
+    << "      <latitude_deg>0</latitude_deg>\n"
+    << "      <longitude_deg>0</longitude_deg>\n"
+    << "      <elevation>0</elevation>\n"
+    << "      <heading_deg>0</heading_deg>\n"
+    << "    </spherical_coordinates>\n"
+    << "    <gravity>0 0 -9.8</gravity>\n"
+    << "    <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>\n"
+    << "    <atmosphere type='adiabatic'/>\n"
+    << "    <physics name='default_physics' default='0' type='ode'>\n"
+    << "      <max_step_size>0.001</max_step_size>\n"
+    << "      <real_time_factor>1</real_time_factor>\n"
+    << "      <real_time_update_rate>1000</real_time_update_rate>\n"
+    << "    </physics>\n"
+    << "    <scene>\n"
+    << "      <ambient>0.4 0.4 0.4 1</ambient>\n"
+    << "      <background>0.7 0.7 0.7 1</background>\n"
+    << "      <shadows>1</shadows>\n"
+    << "    </scene>\n"
+    << "  </world>\n"
+    << "</sdf>\n";
+
+  EXPECT_EQ(root.Element()->ToString("", true, true), stream.str());
+}
diff --git a/test/sdf/empty_road_sph_coords.sdf b/test/sdf/empty_road_sph_coords.sdf
index f9d720d1c..eef134246 100644
--- a/test/sdf/empty_road_sph_coords.sdf
+++ b/test/sdf/empty_road_sph_coords.sdf
@@ -16,7 +16,7 @@
 <!--<gravity>0 0 -9.8</gravity>
     <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>
     <atmosphere type='adiabatic'/>
-    <physics type='ode'>
+    <physics name='default_physics' default='0' type='ode'>
       <max_step_size>0.001</max_step_size>
       <real_time_factor>1</real_time_factor>
       <real_time_update_rate>1000</real_time_update_rate>

From 3ca53c822b32b7c03de67e6fd11e62a5dbcc6e62 Mon Sep 17 00:00:00 2001
From: Ian Chen <ichen@osrfoundation.org>
Date: Wed, 23 Jun 2021 10:18:04 -0700
Subject: [PATCH 2/8] Port particle scatter ratio param to sdf 1.6 (#595)

Signed-off-by: Ian Chen <ichen@osrfoundation.org>
---
 sdf/1.6/particle_emitter.sdf | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sdf/1.6/particle_emitter.sdf b/sdf/1.6/particle_emitter.sdf
index 428ed251e..d6a2fdf7e 100644
--- a/sdf/1.6/particle_emitter.sdf
+++ b/sdf/1.6/particle_emitter.sdf
@@ -104,6 +104,17 @@
     </description>
   </element>
 
+  <element name="particle_scatter_ratio" type="float" default="0.65" required="0">
+    <description>
+    This is used to determine the ratio of particles that will be detected
+    by sensors. Increasing the ratio means there is a higher chance of
+    particles reflecting and interfering with depth sensing, making the
+    emitter appear more dense. Decreasing the ratio decreases the chance
+    of particles reflecting and interfering with depth sensing, making it
+    appear less dense.
+    </description>
+  </element>
+
   <include filename="pose.sdf" required="0"/>
   <include filename="material.sdf" required="0"/>
 </element>

From 11f6b375c403bff6f3cda2d552cb1e167b5c855f Mon Sep 17 00:00:00 2001
From: Jenn Nguyen <jenn@openrobotics.org>
Date: Fri, 25 Jun 2021 13:44:27 -0700
Subject: [PATCH 3/8] Parameter passing prototype (#413)

* check for <experimental:params> & test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* defined xml namespace

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* Param passing prototype: Retrieve specified element (#427)

* retrieve element by identifier under <experimental:params>

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* Moved updateParams before addNestedModel (#464)

* retrieve element for add action & added tests

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* replaced name with element_id

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* moved updateParams before addNestedModel

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* found chars using rfind

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* added error when element_id missing name after ::

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* updated find w/ startIdx

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

Co-authored-by: Addisu Z. Taddese <addisu@openrobotics.org>

* Param passing prototype: Add action (#546)

* tinyxml2 to string helper

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed codecheck errors

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* changed parser_private functions to nonstatic

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed specification check

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action requires 'name' attribute in spec

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed nested include test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed unused param

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* check name attr nonempty

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* storing attribute to variable

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* Param passing prototype: Remove action (#563)

* tinyxml2 to string helper

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed codecheck errors

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* changed parser_private functions to nonstatic

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed specification check

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* remove action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action requires 'name' attribute in spec

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed nested include test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed unused param

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* check name attr nonempty

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* Param passing prototype: Replace action (#566)

* tinyxml2 to string helper

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed codecheck errors

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* changed parser_private functions to nonstatic

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed specification check

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* remove action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action requires 'name' attribute in spec

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed nested include test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed unused param

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* check name attr nonempty

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* replace action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* renamed init element description function

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* added ParamPassing namespace

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* updated add for plugins

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* Param passing prototype: Modify action (#577)

* tinyxml2 to string helper

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed codecheck errors

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* changed parser_private functions to nonstatic

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed specification check

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* remove action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* add action requires 'name' attribute in spec

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed nested include test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed unused param

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* check name attr nonempty

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* replace action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* modify action

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* code cleanup

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* added nested model test

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* readXml wrapper

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* SDFPtr to ElementPtr

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* updated test paths

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* removed nested links

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

* fixed add & modify bugs

Signed-off-by: Jenn Nguyen <jenn@openrobotics.org>

Co-authored-by: Addisu Z. Taddese <addisu@openrobotics.org>
Co-authored-by: Ian Chen <ichen@osrfoundation.org>
---
 include/sdf/Error.hh                          |   2 +-
 src/CMakeLists.txt                            |  16 +
 src/ParamPassing.cc                           | 698 ++++++++++++++++++
 src/ParamPassing.hh                           | 163 ++++
 src/ParamPassing_TEST.cc                      |  93 +++
 src/XmlUtils.cc                               |  16 +-
 src/XmlUtils.hh                               |   5 +
 src/parser.cc                                 |  11 +
 src/parser_private.hh                         |  16 +-
 test/integration/CMakeLists.txt               |   3 +-
 test/integration/include_custom_model.sdf     | 202 +++++
 .../include_custom_model_expected_output.sdf  | 475 ++++++++++++
 ...de_custom_nested_model_expected_output.sdf | 352 +++++++++
 .../include_invalid_custom_model.sdf          | 133 ++++
 test/integration/include_model.sdf            |  10 +
 .../model/nested_include/base/base.sdf        | 158 ++++
 .../model/nested_include/base/model.config    |   6 +
 .../nested_include/test_nested_include.sdf    |  52 ++
 .../nested_include/top_camera/model.config    |   6 +
 .../nested_include/top_camera/top_camera.sdf  |  40 +
 .../nested_include/top_model/model.config     |   5 +
 .../nested_include/top_model/top_model.sdf    |  39 +
 .../model/nested_include/wheel/model.config   |   6 +
 .../model/nested_include/wheel/wheel.sdf      |  38 +
 test/integration/model/robot/model.config     |   5 +
 test/integration/model/robot/model.sdf        | 315 ++++++++
 test/integration/param_passing.cc             | 165 +++++
 27 files changed, 3018 insertions(+), 12 deletions(-)
 create mode 100644 src/ParamPassing.cc
 create mode 100644 src/ParamPassing.hh
 create mode 100644 src/ParamPassing_TEST.cc
 create mode 100644 test/integration/include_custom_model.sdf
 create mode 100644 test/integration/include_custom_model_expected_output.sdf
 create mode 100644 test/integration/include_custom_nested_model_expected_output.sdf
 create mode 100644 test/integration/include_invalid_custom_model.sdf
 create mode 100644 test/integration/include_model.sdf
 create mode 100644 test/integration/model/nested_include/base/base.sdf
 create mode 100644 test/integration/model/nested_include/base/model.config
 create mode 100644 test/integration/model/nested_include/test_nested_include.sdf
 create mode 100644 test/integration/model/nested_include/top_camera/model.config
 create mode 100644 test/integration/model/nested_include/top_camera/top_camera.sdf
 create mode 100644 test/integration/model/nested_include/top_model/model.config
 create mode 100644 test/integration/model/nested_include/top_model/top_model.sdf
 create mode 100644 test/integration/model/nested_include/wheel/model.config
 create mode 100644 test/integration/model/nested_include/wheel/wheel.sdf
 create mode 100644 test/integration/model/robot/model.config
 create mode 100644 test/integration/model/robot/model.sdf
 create mode 100644 test/integration/param_passing.cc

diff --git a/include/sdf/Error.hh b/include/sdf/Error.hh
index 9ae088e9c..ec659ab25 100644
--- a/include/sdf/Error.hh
+++ b/include/sdf/Error.hh
@@ -130,7 +130,7 @@ namespace sdf
     POSE_RELATIVE_TO_GRAPH_ERROR,
 
     /// \brief Indicates that reading an SDF string failed.
-    STRING_READ,
+    STRING_READ
   };
 
   class SDFORMAT_VISIBLE Error
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 9b91292e6..231f5efc9 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -44,6 +44,7 @@ set (sources
   parser.cc
   parser_urdf.cc
   Param.cc
+  ParamPassing.cc
   ParticleEmitter.cc
   Pbr.cc
   Physics.cc
@@ -184,6 +185,21 @@ if (BUILD_SDF_TEST)
     target_link_libraries(UNIT_parser_urdf_TEST PRIVATE
       ${TinyXML2_LIBRARIES})
   endif()
+
+  if (NOT WIN32)
+    set(SDF_BUILD_TESTS_EXTRA_EXE_SRCS ParamPassing.cc XmlUtils.cc parser.cc
+          parser_urdf.cc FrameSemantics.cc Converter.cc EmbeddedSdf.cc SDFExtension.cc)
+    sdf_build_tests(ParamPassing_TEST.cc)
+    if (NOT USE_INTERNAL_URDF)
+      target_compile_options(UNIT_ParamPassing_TEST PRIVATE ${URDF_CFLAGS})
+      if (${CMAKE_VERSION} VERSION_GREATER 3.13)
+        target_link_options(UNIT_ParamPassing_TEST PRIVATE ${URDF_LDFLAGS})
+      endif()
+      target_link_libraries(UNIT_ParamPassing_TEST PRIVATE ${URDF_LIBRARIES})
+    endif()
+    target_link_libraries(UNIT_ParamPassing_TEST PRIVATE
+      ${TinyXML2_LIBRARIES})
+  endif()
 endif()
 
 sdf_add_library(${sdf_target} ${sources})
diff --git a/src/ParamPassing.cc b/src/ParamPassing.cc
new file mode 100644
index 000000000..3278bc292
--- /dev/null
+++ b/src/ParamPassing.cc
@@ -0,0 +1,698 @@
+/*
+ * Copyright 2020 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#include <cstring>
+#include <vector>
+
+#include "sdf/Filesystem.hh"
+#include "sdf/parser.hh"
+#include "sdf/sdf_config.h"
+
+#include "ParamPassing.hh"
+#include "parser_private.hh"
+#include "XmlUtils.hh"
+
+namespace sdf
+{
+inline namespace SDF_VERSION_NAMESPACE {
+namespace ParamPassing {
+
+//////////////////////////////////////////////////
+void updateParams(tinyxml2::XMLElement *_childXmlParams,
+                  ElementPtr _includeSDF, Errors &_errors)
+{
+  // loop through <experimental:params> children
+  tinyxml2::XMLElement *childElemXml = nullptr;
+  for (childElemXml = _childXmlParams->FirstChildElement();
+       childElemXml;
+       childElemXml = childElemXml->NextSiblingElement())
+  {
+    // element identifier
+    const char *childElemId = childElemXml->Attribute("element_id");
+    if (!childElemId)
+    {
+      _errors.push_back({ErrorCode::ATTRIBUTE_MISSING,
+        "Element identifier requires an element_id attribute, but the "
+        "element_id is not set. Skipping element alteration:\n"
+        + ElementToString(childElemXml)
+      });
+      continue;
+    }
+
+    std::string elemIdAttr(childElemId);
+
+    // checks for name after last set of double colons
+    size_t found = elemIdAttr.rfind("::");
+    if (found != std::string::npos
+        && (elemIdAttr.substr(found+2)).empty())
+    {
+      _errors.push_back({ErrorCode::ATTRIBUTE_INVALID,
+        "Missing name after double colons in element identifier. "
+        "Skipping element alteration:\n"
+        + ElementToString(childElemXml)
+      });
+      continue;
+    }
+
+    // *** Retrieve specified element using element identifier ***
+
+    std::string actionStr;
+    if (childElemXml->Attribute("action"))
+    {
+      actionStr = std::string(childElemXml->Attribute("action"));
+
+      if (!isValidAction(actionStr))
+      {
+        _errors.push_back({ErrorCode::ATTRIBUTE_INVALID,
+          "Action [" + actionStr + "] is not a valid action. Skipping "
+          "element alteration:\n" + ElementToString(childElemXml)
+        });
+        continue;
+      }
+    }
+
+    // get element pointer to specified element using element identifier
+    ElementPtr elem;
+
+    if (actionStr == "add")
+    {
+      const char *attr = childElemXml->Attribute("name");
+
+      // checks name attribute exists
+      if (!attr)
+      {
+        _errors.push_back({ErrorCode::ATTRIBUTE_MISSING,
+          "Element to be added is missing a 'name' attribute. "
+          "Skipping element addition:\n"
+          + ElementToString(childElemXml)
+        });
+        continue;
+      }
+
+      // checks name attribute nonempty
+      if (!strlen(attr))
+      {
+        _errors.push_back({ErrorCode::ATTRIBUTE_INVALID,
+          "The 'name' attribute can not be empty. Skipping element addition:\n"
+          + ElementToString(childElemXml)
+        });
+        continue;
+      }
+
+      std::string attrName = attr;
+
+      // check that elem doesn't already exist (except for //plugin)
+      elem  = getElementById(_includeSDF, childElemXml->Name(),
+                            elemIdAttr + "::" + attrName);
+      if (elem != nullptr && elem->GetName() != "plugin")
+      {
+        _errors.push_back({ErrorCode::DUPLICATE_NAME,
+          "Could not add element <" + std::string(childElemXml->Name())
+          + " element_id='" + childElemXml->Attribute("element_id")
+          + "'> because element already exists in included model. "
+          + "Skipping element addition:\n"
+          + ElementToString(childElemXml)
+        });
+        continue;
+      }
+
+      if (elemIdAttr.empty())
+      {
+        // add new element as direct child of included model
+        elem = _includeSDF->GetFirstElement();
+      }
+      else
+      {
+        // get parent element of new element
+        elem = getElementById(_includeSDF, "",
+                              elemIdAttr,
+                              true);
+      }
+    }
+    else
+    {
+      elem  = getElementById(_includeSDF, childElemXml->Name(), elemIdAttr);
+    }
+
+    if (elem == nullptr)
+    {
+      _errors.push_back({ErrorCode::ELEMENT_MISSING,
+        "Could not find element <" + std::string(childElemXml->Name())
+        + " element_id='" + childElemXml->Attribute("element_id") + "'>. " +
+        "Skipping element modification:\n" + ElementToString(childElemXml)
+      });
+      continue;
+    }
+
+    // *** Element modifications ***
+
+    if (actionStr.empty())
+    {
+      // action attribute not in childElemXml so must be in all direct children
+      // of childElemXml
+      handleIndividualChildActions(childElemXml, elem, _errors);
+    }
+    else if (actionStr == "add")
+    {
+      add(childElemXml, elem, _errors);
+    }
+    else if (actionStr == "modify")
+    {
+      modify(childElemXml, elem, _errors);
+    }
+    else if (actionStr == "remove")
+    {
+      remove(childElemXml, elem, _errors);
+    }
+    else if (actionStr == "replace")
+    {
+      ElementPtr newElem = initElementDescription(childElemXml, _errors);
+      if (!newElem)
+        continue;
+
+      if (!xmlToSdf(childElemXml, newElem, _errors))
+      {
+        _errors.push_back({ErrorCode::ELEMENT_INVALID,
+          "Unable to convert XML to SDF. Skipping element replacement:\n"
+          + ElementToString(childElemXml)
+        });
+        continue;
+      }
+
+      replace(newElem, elem);
+    }
+  }
+}
+
+//////////////////////////////////////////////////
+ElementPtr getElementById(const ElementPtr _sdf,
+                          const std::string &_elemName,
+                          const std::string &_elemId,
+                          const bool _isParentElement)
+{
+  // child element of includeSDF
+  ElementPtr childElem = _sdf->GetFirstElement()->GetFirstElement();
+
+  // start and stop idx of elemId for finding longest substring
+  int64_t startIdx = 0, stopIdx = 0, longestIdx = 0;
+  ElementPtr matchingChild = nullptr;
+
+  // iterate through included model
+  while (childElem)
+  {
+    std::string childName;
+    if (childElem->HasAttribute("name"))
+    {
+      childName = childElem->GetAttribute("name")->GetAsString();
+
+      // for add action, found parent element
+      if (_isParentElement && _elemId == childName)
+        return childElem;
+
+      stopIdx = findPrefixLastIndex(_elemId, startIdx, childName);
+
+      if (stopIdx > longestIdx)
+      {
+        matchingChild = childElem;
+
+        // found matching element break out of included model iteration
+        if (!_isParentElement && childElem->GetName() == _elemName
+              && _elemId.substr(startIdx) == childName)
+          break;
+        else if (_isParentElement && _elemId.substr(startIdx) == childName)
+          break;
+
+        longestIdx = stopIdx;
+      }
+    }
+
+    childElem = childElem->GetNextElement();
+
+    // when no more children & found potential match,
+    // set next iteration to first element of match
+    if (!childElem && matchingChild)
+    {
+      childElem = matchingChild->GetFirstElement();
+      matchingChild = nullptr;
+      startIdx = longestIdx;
+
+      size_t found = _elemId.find("::", startIdx);
+      if (found != std::string::npos && (found - startIdx) == 1ul)
+      {
+        // past double colons
+        startIdx += 3;
+      }
+    }
+  }
+
+  // found no element match
+  if (!matchingChild)
+    childElem = nullptr;
+
+  return childElem;
+}
+
+//////////////////////////////////////////////////
+int64_t findPrefixLastIndex(const std::string &_elemId,
+                               const int64_t &_startIdx,
+                               const std::string &_ref)
+{
+  if (_elemId.substr(_startIdx, _ref.size()) == _ref)
+    return _startIdx + (_ref.size()-1);
+
+  return -1;
+}
+
+//////////////////////////////////////////////////
+bool isValidAction(const std::string &_action)
+{
+  return (_action == "add" || _action == "modify"
+          || _action == "remove" || _action == "replace");
+}
+
+//////////////////////////////////////////////////
+ElementPtr getElementByName(const ElementPtr _elem,
+                            const tinyxml2::XMLElement *_xml,
+                            const bool _isModifyAction)
+{
+  std::string elemName = _xml->Name();
+
+  if (!_elem->HasElement(elemName))
+    return nullptr;
+
+  ElementPtr elem = _elem->GetElement(elemName);
+  if (_xml->Attribute("name"))
+  {
+    while (elem != nullptr)
+    {
+      if (elem->HasAttribute("name") &&
+          elem->Get<std::string>("name")
+            == std::string(_xml->Attribute("name")))
+      {
+        return elem;
+      }
+
+      elem = elem->GetNextElement(elemName);
+    }
+
+    // if reached here then element was not found
+    elem = nullptr;
+
+    // if action is modify then 'name' attribute is intended to be added
+    if (_isModifyAction)
+      elem = _elem->GetElement(elemName);
+  }
+  else if (elem->HasAttribute("name")
+            && elem->GetAttribute("name")->GetRequired())
+  {
+    sdfwarn << "The original element [" << elemName << "] contains the "
+            << "attribute 'name' but none was provided in the element modifier."
+            << " The assumed element to be modified is: <" << elemName
+            << " name='" << elem->Get<std::string>("name") << "'>\n";
+  }
+
+  return elem;
+}
+
+//////////////////////////////////////////////////
+ElementPtr initElementDescription(const tinyxml2::XMLElement *_xml,
+                                  Errors &_errors)
+{
+  ElementPtr elemDesc = std::make_shared<Element>();
+  std::string filename = std::string(_xml->Name()) + ".sdf";
+
+  if (!initFile(filename, elemDesc))
+  {
+    // TODO(jenn) not sure if we should load the element anyway
+    // (e.g., user created their own element), maybe future implementation
+    _errors.push_back({ErrorCode::ELEMENT_INVALID,
+      "Element [" + std::string(_xml->Name()) + "] is not a defined "
+      "SDF element. Skipping element alteration\n: "
+      + ElementToString(_xml)
+    });
+    return nullptr;
+  }
+  return elemDesc;
+}
+
+//////////////////////////////////////////////////
+void handleIndividualChildActions(tinyxml2::XMLElement *_childrenXml,
+                                  ElementPtr _elem, Errors &_errors)
+{
+  ElementPtr elemDesc = initElementDescription(_childrenXml, _errors);
+  if (!elemDesc)
+    return;
+
+  // loop through children and handle corresponding actions
+  for (tinyxml2::XMLElement *xmlChild = _childrenXml->FirstChildElement();
+       xmlChild;
+       xmlChild = xmlChild->NextSiblingElement())
+  {
+    if (xmlChild->Attribute("action") == nullptr)
+    {
+      _errors.push_back({ErrorCode::ATTRIBUTE_MISSING,
+        "Missing an action attribute. Skipping child element modification "
+        "with parent <" + std::string(_childrenXml->Name()) + " element_id='"
+        + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+        + ElementToString(xmlChild)
+      });
+      continue;
+    }
+
+    std::string actionStr = xmlChild->Attribute("action");
+    if (!isValidAction(actionStr))
+    {
+      _errors.push_back({ErrorCode::ATTRIBUTE_INVALID,
+        "Action [" + actionStr + "] is not a valid action. Skipping "
+        "child element modification with parent <"
+        + std::string(_childrenXml->Name()) + " element_id='"
+        + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+        + ElementToString(xmlChild)
+      });
+      continue;
+    }
+
+    if (actionStr == "remove")
+    {
+      ElementPtr e = getElementByName(_elem, xmlChild);
+      if (e == nullptr)
+      {
+        _errors.push_back({ErrorCode::ELEMENT_MISSING,
+          "Could not find element. Skipping child element removal "
+          "with parent <" + std::string(_childrenXml->Name()) + " element_id='"
+          + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+          + ElementToString(xmlChild)
+        });
+      }
+      else
+      {
+        remove(xmlChild, e, _errors);
+      }
+
+      continue;
+    }
+    else if (actionStr == "modify")
+    {
+      ElementPtr e = getElementByName(_elem, xmlChild, true);
+      if (e == nullptr)
+      {
+        _errors.push_back({ErrorCode::ELEMENT_MISSING,
+          "Could not find element. Skipping child element modification "
+          "with parent <" + std::string(_childrenXml->Name()) + " element_id='"
+          + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+          + ElementToString(xmlChild)
+        });
+      }
+      else
+      {
+        modify(xmlChild, e, _errors);
+      }
+
+      continue;
+    }
+
+    // get child element description (used for actions: add and replace)
+    std::string elemName = xmlChild->Name();
+
+    // the modification will be skipped if not an existing sdf element
+    // TODO(jenn) not sure if we should load element anyway,
+    // might need to be a future implementation
+    if (!elemDesc->HasElementDescription(elemName))
+    {
+      _errors.push_back({ErrorCode::ELEMENT_INVALID,
+        "Element [" + elemName + "] is not a defined SDF element or is an "
+        "invalid child specification. Skipping "
+        "child element modification with parent <"
+        + std::string(_childrenXml->Name()) + " element_id='"
+        + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+        + ElementToString(xmlChild)
+      });
+      continue;
+    }
+
+    ElementPtr elemChild = elemDesc->GetElementDescription(elemName);
+
+    if (!xmlToSdf(xmlChild, elemChild, _errors))
+    {
+      _errors.push_back({ErrorCode::ELEMENT_INVALID,
+        "Unable to convert XML to SDF. Skipping child element alteration "
+        "with parent <" + std::string(_childrenXml->Name()) + " element_id='"
+        + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+        + ElementToString(xmlChild)
+      });
+      continue;
+    }
+
+    if (actionStr == "add")
+    {
+      _elem->InsertElement(elemChild);
+      elemChild->SetParent(_elem);
+    }
+    else if (actionStr == "replace")
+    {
+      ElementPtr e = getElementByName(_elem, xmlChild);
+      if (e == nullptr)
+      {
+        _errors.push_back({ErrorCode::ELEMENT_MISSING,
+          "Could not find element. Skipping child element replacement "
+          "with parent <" + std::string(_childrenXml->Name()) + " element_id='"
+          + std::string(_childrenXml->Attribute("element_id")) + "'>:\n"
+          + ElementToString(xmlChild)
+        });
+        continue;
+      }
+
+      // check name requirement of original and replacement element
+      if (e->HasAttribute("name") && !xmlChild->Attribute("name"))
+      {
+        _errors.push_back({ErrorCode::ATTRIBUTE_MISSING,
+          "Replacement element is missing a 'name' attribute. "
+          "Skipping element replacement <" + std::string(_childrenXml->Name())
+          + " element_id='" + std::string(_childrenXml->Attribute("element_id"))
+          + "'>:\n" + ElementToString(xmlChild)
+        });
+        continue;
+      }
+
+      replace(elemChild, e);
+    }
+  }
+}
+
+
+//////////////////////////////////////////////////
+void add(tinyxml2::XMLElement *_childXml, ElementPtr _elem, Errors &_errors)
+{
+  ElementPtr newElem = initElementDescription(_childXml, _errors);
+  if (!newElem)
+    return;
+
+  if (xmlToSdf(_childXml, newElem, _errors))
+  {
+    _elem->InsertElement(newElem);
+    newElem->SetParent(_elem);
+  }
+  else
+  {
+    _errors.push_back({ErrorCode::ELEMENT_INVALID,
+      "Unable to convert XML to SDF. Skipping element addition:\n"
+      + ElementToString(_childXml)
+    });
+  }
+}
+
+//////////////////////////////////////////////////
+void modifyAttributes(tinyxml2::XMLElement *_xml,
+                      ElementPtr _elem, Errors &_errors)
+{
+  for (const tinyxml2::XMLAttribute *attr = _xml->FirstAttribute();
+      attr; attr = attr->Next())
+  {
+    std::string attrName = attr->Name();
+
+    if (attrName == "element_id" || attrName == "action")
+      continue;
+
+    if (!_elem->HasAttribute(attrName))
+    {
+      // since custom attribute is not in spec, HasAttribute will always fail
+      // so need to add the attribute whereas other attributes that are part of
+      // the spec HasAttribute will pass even if not set.
+      // TODO(jenn) add attributes for namespaced elements
+      if (attrName.find(":") != std::string::npos)
+      {
+        _elem->AddAttribute(attrName, "string", "", 1, "");
+      }
+      // invalid
+      else
+      {
+        _errors.push_back({ErrorCode::ATTRIBUTE_INVALID,
+          "Attribute [" + attrName + "] is invalid. "
+          "Skipping attribute modification in:\n" + ElementToString(_xml)
+        });
+        continue;
+      }
+    }
+
+    _elem->GetAttribute(attrName)->SetFromString(attr->Value());
+  }
+}
+
+//////////////////////////////////////////////////
+void modifyChildren(tinyxml2::XMLElement *_xml,
+                    ElementPtr _elem, Errors &_errors)
+{
+  for (tinyxml2::XMLElement *xmlChild = _xml->FirstChildElement();
+       xmlChild;
+       xmlChild = xmlChild->NextSiblingElement())
+  {
+    std::string elemName = xmlChild->Name();
+
+    if (!_elem->HasElement(elemName))
+    {
+      _errors.push_back({ErrorCode::ELEMENT_MISSING,
+        "Could not find element [" + elemName + "]. "
+        "Skipping modification for:\n" + ElementToString(_xml)
+      });
+      continue;
+    }
+
+    ElementPtr elemChild = getElementByName(_elem, xmlChild, true);
+    ParamPtr paramChild = elemChild->GetValue();
+
+    if (xmlChild->GetText())
+    {
+      // set xml value to sdf value
+      if (paramChild && !paramChild->SetFromString(xmlChild->GetText()))
+      {
+        _errors.push_back({ErrorCode::ELEMENT_INVALID,
+          "Value [" + std::string(xmlChild->GetText()) + "] for element ["
+          + elemName + "] is invalid. Skipping modification for:\n"
+          + ElementToString(_xml)
+        });
+        continue;
+      }
+
+      modifyAttributes(xmlChild, elemChild, _errors);
+    }
+    else if (xmlChild->NoChildren())
+    {
+      // no value was given
+      if (paramChild)
+      {
+        // if sdf has no child elements, use default value
+        paramChild->SetFromString(paramChild->GetDefaultAsString());
+        modifyAttributes(xmlChild, elemChild, _errors);
+      }
+      else
+      {
+        // sdf has child elements but no children were specified in xml
+        sdfwarn << "No modifications for element "
+                << ElementToString(xmlChild)
+                << " provided, skipping modification for:\n"
+                << ElementToString(_xml) << "\n";
+      }
+    }
+    else
+    {
+      modify(xmlChild, elemChild, _errors);
+    }
+  }
+}
+
+//////////////////////////////////////////////////
+void modify(tinyxml2::XMLElement *_xml, ElementPtr _elem, Errors &_errors)
+{
+  modifyAttributes(_xml, _elem, _errors);
+
+  if (_xml->GetText())
+  {
+    // modify value of element
+    ParamPtr param = _elem->GetValue();
+    if (param && !param->SetFromString(_xml->GetText()))
+    {
+      _errors.push_back({ErrorCode::ELEMENT_INVALID,
+        "Value [" + std::string(_xml->GetText()) + "] for element [" +
+        std::string(_xml->Name()) + "] is invalid. Skipping modification for:\n"
+        + ElementToString(_xml)
+      });
+    }
+  }
+  else
+  {
+    // modify children elements
+    modifyChildren(_xml, _elem, _errors);
+  }
+}
+
+//////////////////////////////////////////////////
+void remove(const tinyxml2::XMLElement *_xml, ElementPtr _elem, Errors &_errors)
+{
+  if (_xml->NoChildren())
+  {
+    _elem->RemoveFromParent();
+  }
+  else
+  {
+    // iterate through children of _xml
+    ElementPtr elemChild = nullptr;
+    const tinyxml2::XMLElement *xmlChild = nullptr;
+    for (xmlChild = _xml->FirstChildElement();
+         xmlChild;
+         xmlChild = xmlChild->NextSiblingElement())
+    {
+      elemChild = getElementByName(_elem, xmlChild);
+      if (elemChild == nullptr)
+      {
+        const tinyxml2::XMLElement *xmlParent = _xml->Parent()->ToElement();
+
+        _errors.push_back({ErrorCode::ELEMENT_MISSING,
+          "Could not find element. Skipping child element removal from <"
+          + std::string(xmlParent->Name()) + " element_id='"
+          + std::string(xmlParent->Attribute("element_id")) + "'> with parent <"
+          + std::string(_xml->Name()) + ">:\n"
+          + ElementToString(xmlChild)
+        });
+        continue;
+      }
+
+      elemChild->RemoveFromParent();
+    }
+  }
+}
+
+//////////////////////////////////////////////////
+void replace(const ElementPtr _newElem, ElementPtr _origElem)
+{
+  if (!_newElem || !_origElem)
+    return;
+
+  _origElem->ClearElements();
+  _origElem->RemoveAllAttributes();
+  _origElem->Copy(_newElem);
+}
+
+//////////////////////////////////////////////////
+bool xmlToSdf(tinyxml2::XMLElement *_xml, ElementPtr _sdf, Errors &_errors)
+{
+  _xml->DeleteAttribute("element_id");
+  _xml->DeleteAttribute("action");
+
+  return readXml(_xml, _sdf, _errors);
+}
+}
+}
+}
diff --git a/src/ParamPassing.hh b/src/ParamPassing.hh
new file mode 100644
index 000000000..4ebd494cb
--- /dev/null
+++ b/src/ParamPassing.hh
@@ -0,0 +1,163 @@
+/*
+ * Copyright 2020 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+*/
+#ifndef SDF_PARAM_PASSING_HH_
+#define SDF_PARAM_PASSING_HH_
+
+#include <tinyxml2.h>
+#include <string>
+
+#include "sdf/SDFImpl.hh"
+#include "sdf/system_util.hh"
+
+namespace sdf
+{
+  // Inline bracket to help doxygen filtering.
+  inline namespace SDF_VERSION_NAMESPACE {
+
+  namespace ParamPassing {
+
+    /// \brief Updates the included model (_includeSDF) with the specified
+    /// modifications listed under //include/experimental:params
+    /// \param[in] _childXmlParams Pointer to //include/experimental:params
+    /// children
+    /// \param[in,out] _includeSDF The loaded (from include) SDF pointer to
+    // parse and update data into
+    /// \param[out] _errors Captures errors found during parsing
+    void updateParams(tinyxml2::XMLElement *_childXmlParams,
+                      ElementPtr _includeSDF, Errors &_errors);
+
+    /// \brief Retrieves the specified element by the element identifier
+    /// and element name
+    /// \param[in] _sdf The loaded (from include) SDF pointer
+    /// \param[in] _elemName The element name, such as "model", "link",
+    /// "collision", "visual".
+    /// \param[in] _elemId The element identifier
+    /// \param[in] _isParentElement Is true if _elemId is the parent and does
+    /// not use _elemName to verify the correct element is found. Only used for
+    /// the add action
+    /// \return ElementPtr to the specified element, nullptr if element could
+    /// not found
+    ElementPtr getElementById(const ElementPtr _sdf,
+                              const std::string &_elemName,
+                              const std::string &_elemId,
+                              const bool _isParentElement = false);
+
+    /// \brief Finds the last index of a matching substring in _elemId from _ref
+    /// \param[in] _elemId The element identifier
+    /// \param[in] _startIdx The starting index for the substring in _elemId
+    /// \param[in] _ref The reference to look for in _elemId
+    /// \return int64_t the last index of the matching prefix in _elemId
+    int64_t findPrefixLastIndex(const std::string &_elemId,
+                                const int64_t &_startIdx,
+                                const std::string &_ref);
+
+    /// \brief Checks if the string is a valid action
+    /// \param[in] _action The action
+    /// \return True if the action is one of the following: add, modify, remove,
+    /// or replace
+    bool isValidAction(const std::string &_action);
+
+    /// \brief Retrieves the sdf element that matches the xml element by element
+    /// name and attribute 'name' if it exists (if the attribute 'name' does
+    /// not exist in the xml then the element is retrieved using only the
+    /// element name)
+    /// \param[in] _elem The sdf (parent) element used to find the matching
+    /// child element described in xml
+    /// \param[in] _xml The xml element to find
+    /// \param[in] _isModifyAction Is true if the action is modify, the
+    /// attribute 'name' may not be in the sdf element (i.e., may be a
+    /// modified/added attribute such as //camera)
+    /// \return ElementPtr to the child element matching the xml, nullptr if
+    /// element could not be found
+    ElementPtr getElementByName(const ElementPtr _elem,
+                                const tinyxml2::XMLElement *_xml,
+                                const bool _isModifyAction = false);
+
+    /// \brief Initialize an sdf element description from the xml element
+    /// \param[in] _xml Pointer to xml element
+    /// \param[out] _errors Captures errors found during parsing
+    /// \return ElementPtr to the initialized element description,
+    /// nullptr if undefined/unknown sdf element
+    ElementPtr initElementDescription(const tinyxml2::XMLElement *_xml,
+                                      Errors &_errors);
+
+    /// \brief Handles individual actions of children in _childrenXml
+    /// \param[in] _childrenXml Pointer to xml element
+    /// \param[out] _elem The sdf element to apply actions
+    /// (i.e., add, modify, remove, replace)
+    /// \param[out] _errors Captures errors found during parsing
+    void handleIndividualChildActions(tinyxml2::XMLElement *_childrenXml,
+                                      ElementPtr _elem, Errors &_errors);
+
+    /// \brief Adds a new element to an element from the included model
+    /// \param[in] _childXml Pointer to the new element to add, which is a child
+    /// of //include/experimental:params
+    /// \param[out] _elem The element from the included model to add the new
+    /// element to
+    /// \param[out] _errors Captures errors found during parsing
+    void add(tinyxml2::XMLElement *_childXml, ElementPtr _elem,
+             Errors &_errors);
+
+    /// \brief Modifies the attributes of an element from the included model
+    /// \param[in] _xml Pointer to the xml element which contains the attributes
+    /// to be modified
+    /// \param[out] _elem The element from the included model to modify the
+    /// attributes to
+    /// \param[out] _errors Captures errors found during parsing
+    void modifyAttributes(tinyxml2::XMLElement *_xml,
+                         ElementPtr _elem, Errors &_errors);
+
+    /// \brief Modifies the children elements of the included model
+    /// \param[in] _xml Pointer to the xml element which contains the elements
+    /// to be modified
+    /// \param[out] _elem The element from the included model to modify
+    void modifyChildren(tinyxml2::XMLElement *_xml,
+                        ElementPtr _elem, Errors &_errors);
+
+    /// \brief Modifies element values and/or attributes of an element from the
+    /// included model
+    /// \param[in] _xml Pointer to the xml element which contains the elements
+    /// to be modified
+    /// \param[out] _elem The element from the included model to modify
+    /// \param[out] _errors Captures errors found during parsing
+    void modify(tinyxml2::XMLElement *_xml, ElementPtr _elem, Errors &_errors);
+
+    /// \brief Removes an element specified in xml
+    /// \param[in] _xml Pointer to the xml element(s) to be removed from _elem
+    /// \param[out] _elem The element from the included model to remove
+    /// elements from
+    /// \param[out] _errors Captures errors found during parsing
+    void remove(const tinyxml2::XMLElement *_xml, ElementPtr _elem,
+                Errors &_errors);
+
+    /// \brief Replace an element with another element
+    /// \param[in] _newElem The replacement element
+    /// \param[out] _origElem The element to be replaced
+    void replace(const ElementPtr _newElem, ElementPtr _origElem);
+
+    /// \brief Wrapper for parser.cc's readXml function, which populates
+    /// an SDF Element from the XML input. The function first strips the
+    /// action and element_id attributes before calling readXml
+    /// \param[in] _xml Pointer to the TinyXML element
+    /// \param[in,out] _sdf SDF pointer to parse data into
+    /// \param[out] _errors Captures errors found during parsing
+    /// \return True on success, false on error
+    bool xmlToSdf(tinyxml2::XMLElement *_xml, ElementPtr _sdf, Errors &_errors);
+  }
+  }
+}
+#endif
diff --git a/src/ParamPassing_TEST.cc b/src/ParamPassing_TEST.cc
new file mode 100644
index 000000000..f9c9a5704
--- /dev/null
+++ b/src/ParamPassing_TEST.cc
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2020 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#include <sstream>
+#include <gtest/gtest.h>
+
+#include "ParamPassing.hh"
+#include "sdf/Element.hh"
+#include "sdf/parser.hh"
+
+/////////////////////////////////////////////////
+TEST(ParamPassing, GetElement)
+{
+  std::ostringstream stream;
+  stream << "<?xml version=\"1.0\"?>"
+         << "<sdf version='1.7'>"
+         << "  <model name='test'>"
+         << "    <model name='test_model'>"
+         << "      <link name='test_link'>"
+         << "        <collision name='test_visual'>"
+         << "          <geometry>"
+         << "            <box>"
+         << "              <size>0.1 0.1 0.1</size>"
+         << "            </box>"
+         << "          </geometry>"
+         << "        </collision>"
+         << "      </link>"
+         << "      <link name='test_link2'>"
+         << "        <visual name='test_visual'>"
+         << "          <geometry>"
+         << "            <box>"
+         << "              <size>0.5 0.5 0.5</size>"
+         << "            </box>"
+         << "          </geometry>"
+         << "        </visual>"
+         << "      </link>"
+         << "    </model>"
+         << "  </model>"
+         << "</sdf>";
+
+  sdf::SDFPtr sdf(new sdf::SDF());
+  sdf::init(sdf);
+  ASSERT_TRUE(sdf::readString(stream.str(), sdf));
+
+  // checking element ptrs to <link name='test_link'> are equal
+  sdf::ElementPtr elem = sdf->Root()->GetFirstElement()
+                                        ->GetElement("model")
+                                        ->GetElement("link");
+  sdf::ElementPtr paramPassElem = sdf::ParamPassing::getElementById(sdf->Root(),
+                                                 "link",
+                                                 "test_model::test_link");
+  EXPECT_NE(nullptr, elem);
+  EXPECT_NE(nullptr, paramPassElem);
+  EXPECT_EQ(elem, paramPassElem);
+
+  // checking element ptrs to <visual name='test_visual'> are equal
+  elem = sdf->Root()->GetFirstElement()
+                        ->GetElement("model")
+                        ->GetElement("link")
+                        ->GetNextElement()
+                        ->GetElement("visual");
+  paramPassElem = sdf::ParamPassing::getElementById(sdf->Root(),
+                                 "visual",
+                                 "test_model::test_link2::test_visual");
+  EXPECT_NE(nullptr, elem);
+  EXPECT_NE(nullptr, paramPassElem);
+  EXPECT_EQ(elem, paramPassElem);
+
+  // No element <visual name='test_visual'> (element is a collision)
+  paramPassElem = sdf::ParamPassing::getElementById(sdf->Root(),
+                                 "visual",
+                                 "test_model::test_link::test_visual");
+  EXPECT_EQ(nullptr, paramPassElem);
+
+  // incorrect element identifier (model::test_link::test_visual)
+  paramPassElem = sdf::ParamPassing::getElementById(sdf->Root(),
+                                 "collision",
+                                 "model::test_link::test_visual");
+  EXPECT_EQ(nullptr, paramPassElem);
+}
diff --git a/src/XmlUtils.cc b/src/XmlUtils.cc
index ff2d86b93..4dbceab71 100644
--- a/src/XmlUtils.cc
+++ b/src/XmlUtils.cc
@@ -55,6 +55,20 @@ tinyxml2::XMLNode *DeepClone(tinyxml2::XMLDocument *_doc,
 
   return copy;
 }
+
+/////////////////////////////////////////////////
+std::string ElementToString(const tinyxml2::XMLElement *_elem)
+{
+  if (_elem == nullptr)
+  {
+    sdferr << "Pointer to XML Element _elem is nullptr\n";
+    return "";
+  }
+
+  tinyxml2::XMLPrinter printer;
+  _elem->Accept(&printer);
+
+  return std::string(printer.CStr());
+}
 }
 }  // namespace sdf
-
diff --git a/src/XmlUtils.hh b/src/XmlUtils.hh
index 82b08b2b9..7ad0c30d4 100644
--- a/src/XmlUtils.hh
+++ b/src/XmlUtils.hh
@@ -40,6 +40,11 @@ namespace sdf
   ///          nullptr if an error occurs.
   tinyxml2::XMLNode *DeepClone(tinyxml2::XMLDocument *_doc,
                                const tinyxml2::XMLNode *_src);
+
+  /// \brief Converts the XML Element to a string
+  /// \param[in] _elem Element to be converted
+  /// \return The string representation
+  std::string ElementToString(const tinyxml2::XMLElement *_elem);
   }
 }
 #endif
diff --git a/src/parser.cc b/src/parser.cc
index a6896ddc1..f79d4c16e 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -37,6 +37,7 @@
 
 #include "Converter.hh"
 #include "FrameSemantics.hh"
+#include "ParamPassing.hh"
 #include "parser_private.hh"
 #include "parser_urdf.hh"
 
@@ -1081,6 +1082,16 @@ bool readXml(tinyxml2::XMLElement *_xml, ElementPtr _sdf, Errors &_errors)
           }
         }
 
+        // TODO(jenn) prototyping parameter passing
+        // ref: sdformat.org > Documentation > Proposal for parameter passing
+        if (elemXml->FirstChildElement("experimental:params"))
+        {
+          ParamPassing::updateParams(
+              elemXml->FirstChildElement("experimental:params"),
+              includeSDF->Root(),
+              _errors);
+        }
+
         if (_sdf->GetName() == "model")
         {
           addNestedModel(_sdf, includeSDF->Root(), _errors);
diff --git a/src/parser_private.hh b/src/parser_private.hh
index 70160004f..f0d920eb2 100644
--- a/src/parser_private.hh
+++ b/src/parser_private.hh
@@ -38,7 +38,7 @@ namespace sdf
   ///            model XML tag
   /// \param[out] _modelFileName file name of the best model file
   /// \return string with the best SDF version supported
-  static std::string getBestSupportedModelVersion(
+  std::string getBestSupportedModelVersion(
       tinyxml2::XMLElement *_modelXML, std::string &_modelFileName);
 
   /// \brief Initialize the SDF interface using a TinyXML2 document.
@@ -47,7 +47,7 @@ namespace sdf
   /// \param[in] _xmlDoc TinyXML2 document containing the SDFormat description
   /// file that corresponds with the input SDFPtr
   /// \param[in] _sdf SDF interface to be initialized
-  static bool initDoc(tinyxml2::XMLDocument *_xmlDoc, SDFPtr _sdf);
+  bool initDoc(tinyxml2::XMLDocument *_xmlDoc, SDFPtr _sdf);
 
   /// \brief Initialize the SDF Element using a TinyXML2 document
   ///
@@ -55,7 +55,7 @@ namespace sdf
   /// \param[in] _xmlDoc TinyXML2 document containing the SDFormat description
   /// file that corresponds with the input ElementPtr
   /// \param[in] _sdf SDF Element to be initialized
-  static bool initDoc(tinyxml2::XMLDocument *_xmlDoc, ElementPtr _sdf);
+  bool initDoc(tinyxml2::XMLDocument *_xmlDoc, ElementPtr _sdf);
 
   /// \brief Initialize the SDF Element by parsing the SDFormat description in
   /// the input TinyXML2 element. This is where SDFormat spec/description files
@@ -64,15 +64,15 @@ namespace sdf
   /// \param[in] _xml TinyXML2 element containing the SDFormat description
   /// file that corresponds with the input ElementPtr
   /// \param[in] _sdf SDF ElementPtr to be initialized
-  static bool initXml(tinyxml2::XMLElement *_xml, ElementPtr _sdf);
+  bool initXml(tinyxml2::XMLElement *_xml, ElementPtr _sdf);
 
   /// \brief Populate the SDF values from a TinyXML document
-  static bool readDoc(tinyxml2::XMLDocument *_xmlDoc, SDFPtr _sdf,
+  bool readDoc(tinyxml2::XMLDocument *_xmlDoc, SDFPtr _sdf,
                       const std::string &_source, bool _convert,
                       Errors &_errors);
 
   /// \brief Populate the SDF values from a TinyXML document
-  static bool readDoc(tinyxml2::XMLDocument *_xmlDoc, ElementPtr _sdf,
+  bool readDoc(tinyxml2::XMLDocument *_xmlDoc, ElementPtr _sdf,
       const std::string &_source, bool _convert, Errors &_errors);
 
   /// \brief Populate an SDF Element from the XML input. The XML input here is
@@ -83,7 +83,7 @@ namespace sdf
   /// \param[in,out] _sdf SDF pointer to parse data into.
   /// \param[out] _errors Captures errors found during parsing.
   /// \return True on success, false on error.
-  static bool readXml(tinyxml2::XMLElement *_xml,
+  bool readXml(tinyxml2::XMLElement *_xml,
                       ElementPtr _sdf,
                       Errors &_errors);
 
@@ -93,7 +93,7 @@ namespace sdf
   /// copied.
   /// \param[in] _onlyUnknown True to copy only elements that are NOT part of
   /// the SDF spec. Set this to false to copy everything.
-  static void copyChildren(ElementPtr _sdf, tinyxml2::XMLElement *_xml,
+  void copyChildren(ElementPtr _sdf, tinyxml2::XMLElement *_xml,
                     const bool _onlyUnknown);
   }
 }
diff --git a/test/integration/CMakeLists.txt b/test/integration/CMakeLists.txt
index 339f801ef..22635b46b 100644
--- a/test/integration/CMakeLists.txt
+++ b/test/integration/CMakeLists.txt
@@ -28,6 +28,7 @@ set(tests
   model_dom.cc
   model_versions.cc
   nested_model.cc
+  param_passing.cc
   parser_error_detection.cc
   particle_emitter_dom.cc
   plugin_attribute.cc
@@ -73,5 +74,3 @@ if (UNIX AND NOT APPLE)
   add_test(NAME INTEGRATION_versioned_symbols
     COMMAND bash ${CMAKE_CURRENT_BINARY_DIR}/all_symbols_have_version.bash ${CMAKE_BINARY_DIR}/src/libsdformat${SDF_MAJOR_VERSION}.so)
 endif()
-
-
diff --git a/test/integration/include_custom_model.sdf b/test/integration/include_custom_model.sdf
new file mode 100644
index 000000000..3cc709e0f
--- /dev/null
+++ b/test/integration/include_custom_model.sdf
@@ -0,0 +1,202 @@
+<?xml version="1.0" ?>
+<sdf version="1.7"
+     xmlns:experimental="http://sdformat.org/schemas/experimental">
+  <world name="world_custom_model">
+    <model name="robot">
+      <include>
+        <uri>robot</uri>
+
+        <experimental:params>
+          <visual element_id="chassis::lidar_visual" action="remove"/>
+          <sensor element_id="chassis::lidar" action="remove"/>
+          <sensor element_id="chassis::camera" action="remove">
+            <always_on/>
+            <visualize/>
+          </sensor>
+
+          <visual element_id="chassis" name="camera_visual" action="add">
+            <pose>-1.06 0 0 0 0 3.14</pose>
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+
+          <link element_id="" name="new_link" action="add">
+            <pose>0 0 0 0 0 0</pose>
+            <sensor type="camera" name="camera_sensor">
+              <camera>
+                <horizontal_fov>1.047</horizontal_fov>
+                <image>
+                  <width>320</width>
+                  <height>240</height>
+                </image>
+                <clip>
+                  <near>0.1</near>
+                  <far>100</far>
+                </clip>
+              </camera>
+              <always_on>1</always_on>
+              <update_rate>30</update_rate>
+              <visualize>true</visualize>
+            </sensor>
+          </link>
+
+          <visual element_id="nested_models::model1::link1" name="new_visual" action="add">
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+
+          <visual element_id="top::camera_visual">
+            <transparency action="add">0.5</transparency>
+            <plugin name="some_visual_plugin" filename="/path/to/plugin" action="add"/>
+            <plugin name="some_visual_plugin" filename="/path/to/plugin" action="add"/>
+
+            <material action="remove">
+              <specular/>
+              <lighting/>
+            </material>
+
+            <geometry action="replace">
+              <sphere>
+                <radius>0.05</radius>
+              </sphere>
+            </geometry>
+
+            <material action="modify">
+              <ambient>0 0 1 1</ambient>
+              <diffuse/>
+            </material>
+          </visual>
+
+          <plugin element_id="top::camera_visual" name="some_visual_plugin" filename="/path/to/plugin" action="add"/>
+
+          <link element_id="top">
+            <collision name="camera_collision" action="remove"/>
+
+            <visual name="top_visual" action="remove">
+              <transparency/>
+              <cast_shadows/>
+              <plugin/>
+              <plugin name="top_plugin3"/>
+            </visual>
+
+            <collision name="top_collision" action="replace">
+              <geometry>
+                <sphere>
+                  <radius>0.65</radius>
+                </sphere>
+              </geometry>
+            </collision>
+
+            <visual name="top_visual" action="modify" custom:test="foo">
+              <geometry>
+                <box>
+                  <size custom:test="bar">1 0.5 0.5</size>
+                </box>
+              </geometry>
+            </visual>
+
+          </link>
+
+          <!-- attribute test get's stripped during replace -->
+          <collision element_id="right_wheel::collision" test="hello" name="right_wheel_collision" action="replace">
+            <geometry>
+              <cylinder>
+                <radius>0.2</radius>
+                <length>0.3</length>
+              </cylinder>
+            </geometry>
+          </collision>
+
+          <!-- attribute custom:test does not get stripped -->
+          <collision element_id="left_wheel::collision" custom:test="hello" name="left_wheel_collision" action="replace">
+            <geometry>
+              <cylinder>
+                <radius>0.2</radius>
+                <length>0.3</length>
+              </cylinder>
+            </geometry>
+          </collision>
+
+          <visual element_id="top::top_visual">
+            <material action="replace">
+              <ambient>0 0 1 1</ambient>
+              <diffuse>0 0 1 1</diffuse>
+            </material>
+          </visual>
+
+          <sensor element_id="top::camera" name="cam" action="modify" custom:test="hello">
+            <pose relative_to="__model__">0.1 0.2 0.3 0 0 0</pose>
+            <topic>top/cam</topic>
+            <update_rate>20</update_rate>
+
+            <camera name="top_camera">
+              <image>
+                <width>1280</width>
+              </image>
+              <clip custom:test="foo">
+                <far>50</far>
+                <near>0.05</near>
+              </clip>
+              <horizontal_fov/>
+            </camera>
+          </sensor>
+
+          <link element_id="caster" action="modify">
+            <pose relative_to="right_wheel"/>
+            <inertial>
+              <mass>0.5</mass>
+              <inertia>
+                <ixx>0.05</ixx>
+                <iyy>0.05</iyy>
+                <izz>0.05</izz>
+              </inertia>
+            </inertial>
+            <visual name="visual">
+              <geometry>
+                <sphere>
+                  <radius>0.8</radius>
+                </sphere>
+              </geometry>
+              <material>
+                <specular>1 1 1 1</specular>
+              </material>
+            </visual>
+            <collision name="collision">
+              <geometry>
+                <sphere>
+                  <radius>0.8</radius>
+                </sphere>
+              </geometry>
+            </collision>
+          </link>
+
+          <model element_id="nested_models">
+            <pose action="modify" relative_to="caster">1 1 1 0 0 0</pose>
+          </model>
+
+          <!-- add link with custom element -->
+          <link element_id="" name="link_custom1" action="add">
+            <foo:custom_elem>
+              foo
+            </foo:custom_elem>
+          </link>
+
+          <link element_id="link_custom1">
+            <!-- modify newly added custom element -->
+            <foo:custom_elem custom:attr="test" action="modify">
+              bar
+            </foo:custom_elem>
+          </link>
+
+        </experimental:params>
+
+      </include>
+    </model>
+  </world>
+</sdf>
diff --git a/test/integration/include_custom_model_expected_output.sdf b/test/integration/include_custom_model_expected_output.sdf
new file mode 100644
index 000000000..9076b37bf
--- /dev/null
+++ b/test/integration/include_custom_model_expected_output.sdf
@@ -0,0 +1,475 @@
+<sdf version='1.7' xmlns:experimental='http://sdformat.org/schemas/experimental'>
+  <world name='world_custom_model'>
+    <model name='robot'>
+
+      <frame name='vehicle::__model__' attached_to='vehicle::chassis'>
+        <pose relative_to='__model__'>0 0 0.325 0 -0 0</pose>
+      </frame>
+
+      <link name='vehicle::chassis'>
+        <pose relative_to='vehicle::__model__'>-0.151427 -0 0.175 0 -0 0</pose>
+        <inertial>
+          <mass>1.14395</mass>
+          <inertia>
+            <ixx>0.126164</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.416519</iyy>
+            <iyz>0</iyz>
+            <izz>0.481014</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <box>
+              <size>2.01142 1 0.568726</size>
+            </box>
+          </geometry>
+          <material>
+            <ambient>0.5 0.5 1 1</ambient>
+            <diffuse>0.5 0.5 1 1</diffuse>
+            <specular>0 0 1 1</specular>
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <box>
+              <size>2.01142 1 0.568726</size>
+            </box>
+          </geometry>
+        </collision>
+
+        <!-- removed -->
+        <!-- <visual name='lidar_visual'>
+          <pose>-0.8 0 0.41 0 -0 0</pose>
+          <geometry>
+            <cylinder>
+              <radius>0.1</radius>
+              <length>0.25</length>
+            </cylinder>
+          </geometry>
+        </visual>
+        <sensor name='lidar' type='gpu_lidar'>
+          <pose>-0.8 0 0.41 0 -0 0</pose>
+          <topic>lidar</topic>
+          <update_rate>10</update_rate>
+          <lidar>
+            <scan>
+              <horizontal>
+                <samples>640</samples>
+                <resolution>1</resolution>
+                <min_angle>-1.39626</min_angle>
+                <max_angle>1.39626</max_angle>
+              </horizontal>
+              <vertical>
+                <samples>16</samples>
+                <resolution>1</resolution>
+                <min_angle>-0.261799</min_angle>
+                <max_angle>0.261799</max_angle>
+              </vertical>
+            </scan>
+            <range>
+              <min>0.08</min>
+              <max>10</max>
+              <resolution>0.01</resolution>
+            </range>
+          </lidar>
+          <visualize>1</visualize>
+          <alwaysOn>1</alwaysOn>
+        </sensor> -->
+
+        <sensor name='camera' type='camera'>
+          <pose>-1.06 0 0 0 -0 3.14</pose>
+          <camera>
+            <horizontal_fov>1.047</horizontal_fov>
+            <image>
+              <width>320</width>
+              <height>240</height>
+            </image>
+            <clip>
+              <near>0.1</near>
+              <far>100</far>
+            </clip>
+          </camera>
+
+          <!-- removed -->
+          <!-- <always_on>1</always_on>
+          <visualize>1</visualize> -->
+
+          <update_rate>30</update_rate>
+          <topic>chassis/camera</topic>
+        </sensor>
+
+        <!-- added -->
+        <visual name='camera_visual'>
+          <pose>-1.06 0 0 0 -0 3.14</pose>
+          <geometry>
+            <box>
+              <size>0.1 0.1 0.1</size>
+            </box>
+          </geometry>
+        </visual>
+      </link>
+
+      <link name='vehicle::top'>
+        <pose relative_to='vehicle::__model__'>0.6 0 0.7 0 -0 0</pose>
+
+        <collision name='top_collision'>
+          <geometry>
+            <sphere>
+              <radius>0.65</radius>
+            </sphere>
+          </geometry>
+        </collision>
+        <!-- replaced with above -->
+        <!-- <collision name='top_collision'>
+          <geometry>
+            <box>
+              <size>0.5 1 0.5</size>
+            </box>
+          </geometry>
+        </collision> -->
+
+        <visual name='top_visual' custom:test='foo'>
+        <!-- modified with above -->
+        <!-- <visual name='top_visual'> -->
+          <geometry>
+            <box>
+              <size custom:test='bar'>1 0.5 0.5</size>
+              <!-- modified with above -->
+              <!-- <size>0.5 1 0.5</size> -->
+            </box>
+          </geometry>
+
+          <material>
+            <ambient>0 0 1 1</ambient>
+            <diffuse>0 0 1 1</diffuse>
+          </material>
+          <!-- replaced with above -->
+          <!-- <material>
+            <ambient>1 0 0 1</ambient>
+            <diffuse>1 0 0 1</diffuse>
+            <specular>1 0 0 1</specular>
+          </material> -->
+
+          <plugin name="top_plugin2" filename="/path/to/plugin"/>
+
+          <!-- removed -->
+          <!-- <transparency>0.5</transparency>
+          <cast_shadows>1</cast_shadows>
+          <plugin name="top_plugin" filename="/path/to/plugin"/>
+          <plugin name="top_plugin3" filename="/path/to/plugin"/> -->
+        </visual>
+
+        <!-- removed -->
+        <!-- <collision name="camera_collision">
+          <pose>-0.2 0 0.3 0 0 3.14</pose>
+          <geometry>
+            <box>
+              <size>0.1 0.1 0.1</size>
+            </box>
+          </geometry>
+        </collision> -->
+
+        <visual name='camera_visual'>
+          <pose>-0.2 0 0.3 0 -0 3.14</pose>
+
+          <geometry>
+            <sphere>
+              <radius>0.05</radius>
+            </sphere>
+          </geometry>
+          <!-- replaced with above -->
+          <!-- <geometry>
+            <box>
+              <size>0.1 0.1 0.1</size>
+            </box>
+          </geometry> -->
+
+          <material>
+            <ambient>0 0 1 1</ambient>
+            <diffuse>0 0 0 1</diffuse>
+            <!-- modified with above -->
+            <!-- <ambient>0 1 0 1</ambient>
+            <diffuse>0 1 0 1</diffuse> -->
+
+            <!-- removed -->
+            <!-- <specular>0.5 0.5 0.5 1</specular>
+            <lighting>1</lighting> -->
+          </material>
+          <plugin name='some_visual_plugin' filename='/path/to/plugin'/>
+
+          <!-- added -->
+          <transparency>0.5</transparency>
+          <plugin name='some_visual_plugin' filename='/path/to/plugin'/>
+          <plugin name='some_visual_plugin' filename='/path/to/plugin'/>
+          <plugin name='some_visual_plugin' filename='/path/to/plugin'/>
+        </visual>
+
+        <sensor name='cam' type='camera' custom:test='hello'>
+          <pose relative_to='vehicle::__model__'>0.1 0.2 0.3 0 -0 0</pose>
+          <camera name='top_camera'>
+        <!-- modified with above -->
+        <!-- <sensor name='camera' type='camera'>
+          <pose>-0.2 0 0.3 0 -0 0</pose>
+          <camera> -->
+            <horizontal_fov>1.047</horizontal_fov>
+            <image>
+              <width>1280</width>
+              <!-- modified with above -->
+              <!-- <width>320</width> -->
+              <height>240</height>
+            </image>
+            <clip custom:test='foo'>
+              <near>0.05</near>
+              <far>50</far>
+            </clip>
+            <!-- modified with above -->
+            <!-- <clip>
+              <near>0.1</near>
+              <far>100</far>
+            </clip> -->
+          </camera>
+          <always_on>1</always_on>
+          <update_rate>20</update_rate>
+          <!-- modified with above -->
+          <!-- <update_rate>30</update_rate> -->
+          <visualize>1</visualize>
+          <topic>top/cam</topic>
+          <!-- modified with above -->
+          <!-- <topic>top/camera</topic> -->
+        </sensor>
+      </link>
+
+      <joint name='vehicle::top_to_base' type='fixed'>
+        <parent>vehicle::chassis</parent>
+        <child>vehicle::top</child>
+      </joint>
+      <link name='vehicle::left_wheel'>
+        <pose relative_to='vehicle::__model__'>0.554283 0.625029 -0.025 -1.5707 0 0</pose>
+        <inertial>
+          <mass>2</mass>
+          <inertia>
+            <ixx>0.145833</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.145833</iyy>
+            <iyz>0</iyz>
+            <izz>0.125</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>0.2 0.2 0.2 1</specular>
+          </material>
+        </visual>
+
+        <collision name='left_wheel_collision' custom:test="hello">
+          <geometry>
+            <cylinder>
+              <radius>0.2</radius>
+              <length>0.3</length>
+            </cylinder>
+          </geometry>
+        </collision>
+        <!-- replaced with above -->
+        <!-- <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+        </collision> -->
+
+      </link>
+      <link name='vehicle::right_wheel'>
+        <pose relative_to='vehicle::__model__'>0.554282 -0.625029 -0.025 -1.5707 0 0</pose>
+        <inertial>
+          <mass>2</mass>
+          <inertia>
+            <ixx>0.145833</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.145833</iyy>
+            <iyz>0</iyz>
+            <izz>0.125</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>0.2 0.2 0.2 1</specular>
+          </material>
+        </visual>
+
+        <collision name='right_wheel_collision'>
+          <geometry>
+            <cylinder>
+              <radius>0.2</radius>
+              <length>0.3</length>
+            </cylinder>
+          </geometry>
+        </collision>
+        <!-- replaced with above -->
+        <!-- <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+        </collision> -->
+
+      </link>
+      <link name='vehicle::caster'>
+        <pose relative_to='vehicle::right_wheel'>0 0 0 0 0 0</pose>
+        <!-- modified with above -->
+        <!-- <pose relative_to='vehicle::__model__'>-0.957138 -0 -0.125 0 -0 0</pose> -->
+        <inertial>
+          <mass>0.5</mass>
+          <!-- modified with above -->
+          <!-- <mass>1</mass> -->
+          <inertia>
+            <ixx>0.05</ixx>
+            <!-- modified with above -->
+            <!-- <ixx>0.1</ixx> -->
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.05</iyy>
+            <!-- modified with above -->
+            <!-- <iyy>0.1</iyy> -->
+            <iyz>0</iyz>
+            <izz>0.05</izz>
+            <!-- modified with above -->
+            <!-- <izz>0.1</izz> -->
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.8</radius>
+              <!-- modified with above -->
+              <!-- <radius>0.2</radius> -->
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>1 1 1 1</specular>
+            <!-- modified with above -->
+            <!-- <specular>0.2 0.2 0.2 1</specular> -->
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.8</radius>
+              <!-- modified with above -->
+              <!-- <radius>0.2</radius> -->
+            </sphere>
+          </geometry>
+        </collision>
+      </link>
+      <joint name='vehicle::left_wheel_joint' type='revolute'>
+        <parent>vehicle::chassis</parent>
+        <child>vehicle::left_wheel</child>
+        <axis>
+          <xyz>0 0 1</xyz>
+          <limit>
+            <lower>-1.79769e+308</lower>
+            <upper>1.79769e+308</upper>
+          </limit>
+        </axis>
+      </joint>
+      <joint name='vehicle::right_wheel_joint' type='revolute'>
+        <parent>vehicle::chassis</parent>
+        <child>vehicle::right_wheel</child>
+        <axis>
+          <xyz>0 0 1</xyz>
+          <limit>
+            <lower>-1.79769e+308</lower>
+            <upper>1.79769e+308</upper>
+          </limit>
+        </axis>
+      </joint>
+      <joint name='vehicle::caster_wheel' type='ball'>
+        <parent>vehicle::chassis</parent>
+        <child>vehicle::caster</child>
+      </joint>
+
+      <model name='vehicle::nested_models'>
+        <pose relative_to='vehicle::caster'>1 1 1 0 -0 0</pose>
+        <!-- modified with above -->
+        <!-- <pose relative_to='vehicle::__model__'>0 0 0 0 -0 0</pose> -->
+        <model name='model1'>
+          <link name='link1'>
+
+            <!-- added -->
+            <visual name='new_visual'>
+              <geometry>
+                <box>
+                  <size>0.1 0.1 0.1</size>
+                </box>
+              </geometry>
+            </visual>
+
+          </link>
+        </model>
+      </model>
+
+      <!-- added -->
+      <link name='vehicle::new_link'>
+        <pose relative_to='vehicle::__model__'>0 0 0 0 -0 0</pose>
+        <sensor name='camera_sensor' type='camera'>
+          <camera>
+            <horizontal_fov>1.047</horizontal_fov>
+            <image>
+              <width>320</width>
+              <height>240</height>
+            </image>
+            <clip>
+              <near>0.1</near>
+              <far>100</far>
+            </clip>
+          </camera>
+          <always_on>1</always_on>
+          <update_rate>30</update_rate>
+          <visualize>1</visualize>
+        </sensor>
+      </link>
+
+      <!-- added -->
+      <link name="vehicle::link_custom1">
+        <pose relative_to='vehicle::__model__'>0 0 0 0 -0 0</pose>
+        <!-- modified value from foo to bar-->
+        <foo:custom_elem custom:attr='test'>bar</foo:custom_elem>
+      </link>
+
+    </model>
+    <gravity>0 0 -9.8</gravity>
+    <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>
+    <atmosphere type='adiabatic'/>
+    <physics type='ode'>
+      <max_step_size>0.001</max_step_size>
+      <real_time_factor>1</real_time_factor>
+      <real_time_update_rate>1000</real_time_update_rate>
+    </physics>
+    <scene>
+      <ambient>0.4 0.4 0.4 1</ambient>
+      <background>0.7 0.7 0.7 1</background>
+      <shadows>1</shadows>
+    </scene>
+  </world>
+</sdf>
diff --git a/test/integration/include_custom_nested_model_expected_output.sdf b/test/integration/include_custom_nested_model_expected_output.sdf
new file mode 100644
index 000000000..533528b8b
--- /dev/null
+++ b/test/integration/include_custom_nested_model_expected_output.sdf
@@ -0,0 +1,352 @@
+<sdf version='1.7'>
+  <world name='world_custom_model'>
+    <model name='robot'>
+      <frame name='base::__model__' attached_to='base::chassis'>
+        <pose relative_to='__model__'>0 0 0.325 0 -0 0</pose>
+      </frame>
+      <link name='base::chassis'>
+        <pose relative_to='base::__model__'>-0.151427 -0 0.175 0 -0 0</pose>
+        <inertial>
+          <mass>1.14395</mass>
+          <inertia>
+            <ixx>0.126164</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.416519</iyy>
+            <iyz>0</iyz>
+            <izz>0.481014</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <box>
+              <size>2.01142 1 0.568726</size>
+            </box>
+          </geometry>
+          <material>
+            <ambient>0.5 0.5 1 1</ambient>
+            <diffuse>0.5 0.5 1 1</diffuse>
+            <specular>0 0 1 1</specular>
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <box>
+              <size>2.01142 1 0.568726</size>
+            </box>
+          </geometry>
+        </collision>
+
+        <!-- removed -->
+        <!-- <visual name='lidar_visual'>
+          <pose>-0.8 0 0.41 0 -0 0</pose>
+          <geometry>
+            <cylinder>
+              <radius>0.1</radius>
+              <length>0.25</length>
+            </cylinder>
+          </geometry>
+        </visual> -->
+
+        <!-- removed -->
+        <!-- <sensor name='lidar' type='gpu_lidar'>
+          <pose>-0.8 0 0.41 0 -0 0</pose>
+          <topic>lidar</topic>
+          <update_rate>10</update_rate>
+          <lidar>
+            <scan>
+              <horizontal>
+                <samples>640</samples>
+                <resolution>1</resolution>
+                <min_angle>-1.39626</min_angle>
+                <max_angle>1.39626</max_angle>
+              </horizontal>
+              <vertical>
+                <samples>16</samples>
+                <resolution>1</resolution>
+                <min_angle>-0.261799</min_angle>
+                <max_angle>0.261799</max_angle>
+              </vertical>
+            </scan>
+            <range>
+              <min>0.08</min>
+              <max>10</max>
+              <resolution>0.01</resolution>
+            </range>
+          </lidar>
+          <visualize>1</visualize>
+          <alwaysOn>1</alwaysOn>
+        </sensor> -->
+
+        <sensor name='camera' type='camera'>
+          <pose>-1.06 0 0 0 -0 3.14</pose>
+          <camera>
+            <horizontal_fov>1.047</horizontal_fov>
+            <image>
+              <width>320</width>
+              <height>240</height>
+            </image>
+            <clip>
+              <near>0.1</near>
+              <far>100</far>
+            </clip>
+          </camera>
+          <always_on>1</always_on>
+          <update_rate>30</update_rate>
+          <visualize>1</visualize>
+          <topic>chassis/camera</topic>
+        </sensor>
+
+        <!-- added -->
+        <visual name="camera_visual">
+          <pose>-1.06 0 0 0 -0 3.14</pose>
+          <geometry>
+            <box>
+              <size>0.1 0.1 0.1</size>
+            </box>
+          </geometry>
+        </visual>
+      </link>
+      <frame name='base::top_model::__model__' attached_to='base::top_model::top'>
+        <pose relative_to='base::__model__'>0 0 0 0 -0 0</pose>
+      </frame>
+      <link name='base::top_model::top'>
+        <pose relative_to='base::top_model::__model__'>0.6 0 0.7 0 -0 0</pose>
+        <collision name='top_collision'>
+          <geometry>
+            <box>
+              <size>0.5 1 0.5</size>
+            </box>
+          </geometry>
+        </collision>
+        <visual name='top_visual'>
+          <geometry>
+            <box>
+              <size>0.5 1 0.5</size>
+            </box>
+          </geometry>
+          <material>
+            <ambient>1 0 0 1</ambient>
+            <diffuse>1 0 0 1</diffuse>
+            <specular>1 0 0 1</specular>
+          </material>
+        </visual>
+      </link>
+      <frame name='base::top_model::top_camera::__model__' attached_to='base::top_model::top_camera::top_camera_link'>
+        <pose relative_to='base::top_model::top'>0 0 0 0 -0 0</pose>
+      </frame>
+      <link name='base::top_model::top_camera::top_camera_link'>
+        <visual name='camera_visual'>
+          <pose>-0.2 0 0.3 0 -0 3.14</pose>
+          <geometry>
+            <sphere>
+              <radius>0.05</radius>
+            </sphere>
+          </geometry>
+          <!-- replaced with above -->
+          <!-- <geometry>
+            <box>
+              <size>0.1 0.1 0.1</size>
+            </box>
+          </geometry> -->
+          <material>
+            <ambient>0 0 1 1</ambient>
+            <diffuse>0 0 1 1</diffuse>
+            <!-- modified with above -->
+            <!-- <ambient>0 1 0 1</ambient>
+            <diffuse>0 1 0 1</diffuse> -->
+            <specular>0.5 0.5 0.5 1</specular>
+          </material>
+        </visual>
+        <sensor name='camera' type='camera'>
+          <pose>0 0 0 0 -0 3.14</pose>
+          <!-- modified with above -->
+          <!-- <pose>-0.2 0 0.3 0 -0 0</pose> -->
+          <camera>
+            <horizontal_fov>1.047</horizontal_fov>
+            <image>
+              <width>320</width>
+              <height>240</height>
+            </image>
+            <clip>
+              <near>0.1</near>
+              <far>100</far>
+            </clip>
+          </camera>
+          <always_on>1</always_on>
+          <update_rate>60</update_rate>
+          <!-- modified with above -->
+          <!-- <update_rate>30</update_rate> -->
+          <visualize>1</visualize>
+          <topic>top/camera</topic>
+        </sensor>
+        <pose relative_to='base::top_model::top_camera::__model__'>0 0 0 0 -0 0</pose>
+
+        <!-- added -->
+        <collision name="camera_collision">
+          <pose>-0.2 0 0.3 0 0 3.14</pose>
+          <geometry>
+            <sphere>
+              <radius>0.05</radius>
+            </sphere>
+          </geometry>
+        </collision>
+      </link>
+      <joint name='base::top_model::top_to_camera' type='fixed'>
+        <parent>base::top_model::top</parent>
+        <child>base::top_model::top_camera::top_camera_link</child>
+      </joint>
+      <joint name='base::top_to_base' type='fixed'>
+        <parent>base::chassis</parent>
+        <child>base::top_model::top</child>
+      </joint>
+      <frame name='base::left_wheel::__model__' attached_to='base::left_wheel::wheel_link'>
+        <pose relative_to='base::__model__'>0.554283 0.625029 -0.025 -1.5707 0 0</pose>
+      </frame>
+      <link name='base::left_wheel::wheel_link'>
+        <pose relative_to='base::left_wheel::__model__'>0 0 0 0 -0 0</pose>
+        <inertial>
+          <mass>2</mass>
+          <inertia>
+            <ixx>0.145833</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.145833</iyy>
+            <iyz>0</iyz>
+            <izz>0.125</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>0.2 0.2 0.2 1</specular>
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+        </collision>
+      </link>
+      <frame name='base::right_wheel::__model__' attached_to='base::right_wheel::wheel_link'>
+        <pose relative_to='base::__model__'>0.554282 -0.625029 -0.025 -1.5707 0 0</pose>
+      </frame>
+      <link name='base::right_wheel::wheel_link'>
+        <pose relative_to='base::right_wheel::__model__'>0 0 0 0 -0 0</pose>
+        <inertial>
+          <mass>2</mass>
+          <inertia>
+            <ixx>0.145833</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.145833</iyy>
+            <iyz>0</iyz>
+            <izz>0.125</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>0.2 0.2 0.2 1</specular>
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+        </collision>
+      </link>
+      <frame name='base::caster::__model__' attached_to='base::caster::wheel_link'>
+        <pose relative_to='base::__model__'>-0.957138 -0 -0.025 0 -0 0</pose>
+      </frame>
+      <link name='base::caster::wheel_link'>
+        <pose relative_to='base::caster::__model__'>0 0 0 0 -0 0</pose>
+        <inertial>
+          <mass>2</mass>
+          <inertia>
+            <ixx>0.145833</ixx>
+            <ixy>0</ixy>
+            <ixz>0</ixz>
+            <iyy>0.145833</iyy>
+            <iyz>0</iyz>
+            <izz>0.125</izz>
+          </inertia>
+        </inertial>
+        <visual name='visual'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <ambient>0.2 0.2 0.2 1</ambient>
+            <diffuse>0.2 0.2 0.2 1</diffuse>
+            <specular>0.2 0.2 0.2 1</specular>
+          </material>
+        </visual>
+        <collision name='collision'>
+          <geometry>
+            <sphere>
+              <radius>0.3</radius>
+            </sphere>
+          </geometry>
+        </collision>
+      </link>
+      <joint name='base::left_wheel_joint' type='revolute'>
+        <parent>base::chassis</parent>
+        <child>base::left_wheel::wheel_link</child>
+        <axis>
+          <xyz>0 0 1</xyz>
+          <limit>
+            <lower>-1.79769e+308</lower>
+            <upper>1.79769e+308</upper>
+          </limit>
+        </axis>
+      </joint>
+      <joint name='base::right_wheel_joint' type='revolute'>
+        <parent>base::chassis</parent>
+        <child>base::right_wheel::wheel_link</child>
+        <axis>
+          <xyz>0 0 1</xyz>
+          <limit>
+            <lower>-1.79769e+308</lower>
+            <upper>1.79769e+308</upper>
+          </limit>
+        </axis>
+      </joint>
+      <joint name='base::caster_wheel' type='ball'>
+        <parent>base::chassis</parent>
+        <child>base::caster::wheel_link</child>
+      </joint>
+    </model>
+    <gravity>0 0 -9.8</gravity>
+    <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>
+    <atmosphere type='adiabatic'/>
+    <physics type='ode'>
+      <max_step_size>0.001</max_step_size>
+      <real_time_factor>1</real_time_factor>
+      <real_time_update_rate>1000</real_time_update_rate>
+    </physics>
+    <scene>
+      <ambient>0.4 0.4 0.4 1</ambient>
+      <background>0.7 0.7 0.7 1</background>
+      <shadows>1</shadows>
+    </scene>
+  </world>
+</sdf>
diff --git a/test/integration/include_invalid_custom_model.sdf b/test/integration/include_invalid_custom_model.sdf
new file mode 100644
index 000000000..c1a95f3b7
--- /dev/null
+++ b/test/integration/include_invalid_custom_model.sdf
@@ -0,0 +1,133 @@
+<?xml version="1.0" ?>
+<sdf version="1.7"
+     xmlns:experimental="http://sdformat.org/schemas/experimental">
+  <world name="world_invalid_custom_model">
+    <model name="robot">
+      <include>
+        <uri>robot</uri>
+        <experimental:params>
+          <!-- missing element_id attribute (i.e., element identifier) -->
+          <foo/>
+          <!-- element does not exist -->
+          <visual element_id="chassis::camera_visual" action="modify">
+            <pose>-1.06 0 0 0 0 3.14</pose>
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+          <!-- element already exists -->
+          <visual element_id="chassis" name="visual" action="add">
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+          <!-- parent of new element does not exist -->
+          <visual element_id="chassis::test" name="visual" action="add">
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+          <!-- missing name after :: -->
+          <link element_id="chassis::test::" name="foo" action="add"/>
+
+          <visual element_id="top::camera_visual">
+            <!-- missing action attribute -->
+            <transparency>0.2</transparency>
+
+            <!-- incorrect schema (missing required attributes) -->
+            <plugin action="add"/>
+
+            <!-- not defined sdf element -->
+            <test action="add"/>
+          </visual>
+
+          <!-- not defined sdf element -->
+          <test element_id="chassis" name="new_elem" action="add"/>
+
+          <!-- missing 'name' attribute -->
+          <plugin element_id="chassis" action="add"/>
+
+          <!-- 'name' attribute is empty -->
+          <plugin element_id="chassis" name="" action="add"/>
+
+          <!-- incorrect schema (missing required 'filename' attribute) -->
+          <plugin element_id="chassis" name="some_plugin" action="add"/>
+
+          <!-- invalid action -->
+          <link element_id="top" action="test"/>
+
+          <collision element_id="left_wheel::collision">
+            <!-- invalid child action -->
+            <geometry action="test"/>
+
+            <!-- child element does not exist -->
+            <laser_retro action="remove"/>
+
+            <!-- child <box> (child of <geometry>) does not exist -->
+            <geometry action="remove">
+              <box/>
+            </geometry>
+          </collision>
+
+          <link element_id="top">
+            <!-- child element (w/ name attribute) does not exist -->
+            <collision name="collision" action="remove"/>
+
+            <!-- child element does not exist -->
+            <collision name="collision" action="replace"/>
+
+            <!-- missing 'name' attribute -->
+            <collision action="replace"/>
+
+            <!-- invalid attribute -->
+            <collision name="top_collision" action="modify" test="foo"/>
+
+            <!-- element missing -->
+            <geometry action="modify">
+              <box>
+                <size>1 1 1</size>
+              </box>
+            </geometry>
+
+          </link>
+
+          <!-- incorrect schema (missing required 'type' attribute) -->
+          <sensor element_id="chassis::camera" name="camera" action="replace"/>
+
+          <!-- invalid attribute -->
+          <link element_id="top" action="modify" test="foo">
+
+            <!-- element missing -->
+            <inertial/>
+
+            <collision name="top_collision">
+              <!-- element missing -->
+              <geometry>
+                <sphere>
+                  <radius>0.5</radius>
+                </sphere>
+              </geometry>
+
+              <!-- element has invalid value -->
+              <geometry>
+                <box>
+                  <size>0.5 0.5</size>
+                </box>
+              </geometry>
+
+              <!-- no modifications listed, warning is printed (not error) -->
+              <geometry/>
+            </collision>
+          </link>
+
+        </experimental:params>
+      </include>
+    </model>
+  </world>
+</sdf>
diff --git a/test/integration/include_model.sdf b/test/integration/include_model.sdf
new file mode 100644
index 000000000..f644f6cc7
--- /dev/null
+++ b/test/integration/include_model.sdf
@@ -0,0 +1,10 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <world name="world_model">
+    <model name="robot">
+      <include>
+        <uri>robot</uri>
+      </include>
+    </model>
+  </world>
+</sdf>
diff --git a/test/integration/model/nested_include/base/base.sdf b/test/integration/model/nested_include/base/base.sdf
new file mode 100644
index 000000000..18827b3b2
--- /dev/null
+++ b/test/integration/model/nested_include/base/base.sdf
@@ -0,0 +1,158 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <model name="base">
+    <pose>0 0 0.325 0 -0 0</pose>
+
+    <link name='chassis'>
+      <pose>-0.151427 -0 0.175 0 -0 0</pose>
+      <inertial>
+        <mass>1.14395</mass>
+        <inertia>
+          <ixx>0.126164</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.416519</iyy>
+          <iyz>0</iyz>
+          <izz>0.481014</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <box>
+            <size>2.01142 1 0.568726</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>0.5 0.5 1.0 1</ambient>
+          <diffuse>0.5 0.5 1.0 1</diffuse>
+          <specular>0.0 0.0 1.0 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <box>
+            <size>2.01142 1 0.568726</size>
+          </box>
+        </geometry>
+      </collision>
+
+      <visual name="lidar_visual">
+        <pose>-0.8 0 0.41 0 0 0</pose>
+          <geometry>
+              <cylinder>
+                  <radius>0.1</radius>
+                  <length>0.25</length>
+              </cylinder>
+          </geometry>
+      </visual>
+
+      <sensor name='lidar' type='gpu_lidar'>
+        <pose>-0.8 0 0.41 0 0 0</pose>
+        <topic>lidar</topic>
+        <update_rate>10</update_rate>
+        <lidar>
+          <scan>
+            <horizontal>
+              <samples>640</samples>
+              <resolution>1</resolution>
+              <min_angle>-1.396263</min_angle>
+              <max_angle>1.396263</max_angle>
+            </horizontal>
+            <vertical>
+              <samples>16</samples>
+              <resolution>1</resolution>
+              <min_angle>-0.261799</min_angle>
+              <max_angle>0.261799</max_angle>
+            </vertical>
+          </scan>
+          <range>
+            <min>0.08</min>
+            <max>10.0</max>
+            <resolution>0.01</resolution>
+          </range>
+        </lidar>
+        <alwaysOn>1</alwaysOn>
+        <visualize>true</visualize>
+      </sensor>
+
+      <sensor name="camera" type="camera">
+        <pose>-1.06 0 0 0 0 3.14</pose>
+        <camera>
+          <horizontal_fov>1.047</horizontal_fov>
+          <image>
+            <width>320</width>
+            <height>240</height>
+          </image>
+          <clip>
+            <near>0.1</near>
+            <far>100</far>
+          </clip>
+        </camera>
+        <always_on>1</always_on>
+        <update_rate>30</update_rate>
+        <visualize>true</visualize>
+        <topic>chassis/camera</topic>
+      </sensor>
+
+    </link>
+
+    <include>
+      <uri>top_model</uri>
+    </include>
+
+    <joint name="top_to_base" type="fixed">
+      <parent>chassis</parent>
+      <child>top_model::top</child>
+    </joint>
+
+    <include>
+      <uri>wheel</uri>
+      <pose>0.554283 0.625029 -0.025 -1.5707 0 0</pose>
+      <name>left_wheel</name>
+    </include>
+
+    <include>
+      <uri>wheel</uri>
+      <pose>0.554282 -0.625029 -0.025 -1.5707 0 0</pose>
+      <name>right_wheel</name>
+    </include>
+
+    <include>
+      <uri>wheel</uri>
+      <pose>-0.957138 -0 -0.025 0 -0 0</pose>
+      <name>caster</name>
+    </include>
+
+
+    <joint name='left_wheel_joint' type='revolute'>
+      <parent>chassis</parent>
+      <child>left_wheel::wheel_link</child>
+      <axis>
+        <xyz>0 0 1</xyz>
+        <limit>
+          <lower>-1.79769e+308</lower>
+          <upper>1.79769e+308</upper>
+        </limit>
+      </axis>
+    </joint>
+
+
+    <joint name='right_wheel_joint' type='revolute'>
+      <parent>chassis</parent>
+      <child>right_wheel::wheel_link</child>
+      <axis>
+        <xyz>0 0 1</xyz>
+        <limit>
+          <lower>-1.79769e+308</lower>
+          <upper>1.79769e+308</upper>
+        </limit>
+      </axis>
+    </joint>
+
+    <joint name='caster_wheel' type='ball'>
+      <parent>chassis</parent>
+      <child>caster::wheel_link</child>
+    </joint>
+
+  </model>
+</sdf>
diff --git a/test/integration/model/nested_include/base/model.config b/test/integration/model/nested_include/base/model.config
new file mode 100644
index 000000000..9cad6b4e0
--- /dev/null
+++ b/test/integration/model/nested_include/base/model.config
@@ -0,0 +1,6 @@
+<?xml version="1.0"?>
+<model>
+  <name>base</name>
+  <sdf version="1.7">base.sdf</sdf>
+</model>
+
diff --git a/test/integration/model/nested_include/test_nested_include.sdf b/test/integration/model/nested_include/test_nested_include.sdf
new file mode 100644
index 000000000..744d3f294
--- /dev/null
+++ b/test/integration/model/nested_include/test_nested_include.sdf
@@ -0,0 +1,52 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <world name="world_custom_model">
+    <model name="robot">
+      <include>
+        <uri>base</uri>
+
+        <experimental:params>
+          <visual element_id="chassis::lidar_visual" action="remove"/>
+          <sensor element_id="chassis::lidar" action="remove"/>
+
+          <visual element_id="chassis" name="camera_visual" action="add">
+            <pose>-1.06 0 0 0 0 3.14</pose>
+            <geometry>
+              <box>
+                <size>0.1 0.1 0.1</size>
+              </box>
+            </geometry>
+          </visual>
+
+          <sensor element_id="top_model::top_camera::top_camera_link::camera" action="modify">
+            <pose>0 0 0 0 0 3.14</pose>
+            <update_rate>60</update_rate>
+          </sensor>
+
+          <visual element_id="top_model::top_camera::top_camera_link::camera_visual">
+            <geometry action="replace">
+              <sphere>
+                <radius>0.05</radius>
+              </sphere>
+            </geometry>
+            <material action="modify">
+              <!-- blue -->
+              <ambient>0 0 1 1</ambient>
+              <diffuse>0 0 1 1</diffuse>
+            </material>
+          </visual>
+
+          <collision element_id="top_model::top_camera::top_camera_link" name="camera_collision" action="add">
+            <pose>-0.2 0 0.3 0 0 3.14</pose>
+            <geometry>
+              <sphere>
+                <radius>0.05</radius>
+              </sphere>
+            </geometry>
+          </collision>
+        </experimental:params>
+      </include>
+    </model>
+
+  </world>
+</sdf>
diff --git a/test/integration/model/nested_include/top_camera/model.config b/test/integration/model/nested_include/top_camera/model.config
new file mode 100644
index 000000000..19b6749b2
--- /dev/null
+++ b/test/integration/model/nested_include/top_camera/model.config
@@ -0,0 +1,6 @@
+<?xml version="1.0"?>
+<model>
+  <name>top_camera</name>
+  <sdf version="1.7">top_camera.sdf</sdf>
+</model>
+
diff --git a/test/integration/model/nested_include/top_camera/top_camera.sdf b/test/integration/model/nested_include/top_camera/top_camera.sdf
new file mode 100644
index 000000000..b871cbfdf
--- /dev/null
+++ b/test/integration/model/nested_include/top_camera/top_camera.sdf
@@ -0,0 +1,40 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <model name='top_camera'>
+
+    <link name="top_camera_link">
+      <visual name="camera_visual">
+        <pose>-0.2 0 0.3 0 0 3.14</pose>
+        <geometry>
+          <box>
+            <size>0.1 0.1 0.1</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>0 1 0 1</ambient>
+          <diffuse>0 1 0 1</diffuse>
+          <specular>0.5 0.5 0.5 1</specular>
+        </material>
+      </visual>
+
+      <sensor name="camera" type="camera">
+        <pose>-0.2 0 0.3 0 0.0 0</pose>
+        <camera>
+          <horizontal_fov>1.047</horizontal_fov>
+          <image>
+            <width>320</width>
+            <height>240</height>
+          </image>
+          <clip>
+            <near>0.1</near>
+            <far>100</far>
+          </clip>
+        </camera>
+        <always_on>1</always_on>
+        <update_rate>30</update_rate>
+        <visualize>true</visualize>
+        <topic>top/camera</topic>
+      </sensor>
+    </link>
+  </model>
+</sdf>
diff --git a/test/integration/model/nested_include/top_model/model.config b/test/integration/model/nested_include/top_model/model.config
new file mode 100644
index 000000000..fbe7b28ad
--- /dev/null
+++ b/test/integration/model/nested_include/top_model/model.config
@@ -0,0 +1,5 @@
+<?xml version="1.0"?>
+<model>
+  <name>top_model</name>
+  <sdf version="1.7">top_model.sdf</sdf>
+</model>
diff --git a/test/integration/model/nested_include/top_model/top_model.sdf b/test/integration/model/nested_include/top_model/top_model.sdf
new file mode 100644
index 000000000..19131e51b
--- /dev/null
+++ b/test/integration/model/nested_include/top_model/top_model.sdf
@@ -0,0 +1,39 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <model name='top_model'>
+
+    <link name="top">
+      <pose>0.6 0 0.7 0 0 0</pose>
+      <collision name="top_collision">
+        <geometry>
+          <box>
+            <size>0.5 1 0.5</size>
+          </box>
+        </geometry>
+      </collision>
+      <visual name="top_visual">
+        <geometry>
+          <box>
+            <size>0.5 1 0.5</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>1 0 0 1</ambient>
+          <diffuse>1 0 0 1</diffuse>
+          <specular>1 0 0 1</specular>
+        </material>
+      </visual>
+    </link>
+
+    <include>
+      <uri>top_camera</uri>
+      <pose relative_to="top">0 0 0 0 0 0</pose>
+    </include>
+
+    <joint name="top_to_camera" type="fixed">
+      <parent>top</parent>
+      <child>top_camera::top_camera_link</child>
+    </joint>
+
+  </model>
+</sdf>
diff --git a/test/integration/model/nested_include/wheel/model.config b/test/integration/model/nested_include/wheel/model.config
new file mode 100644
index 000000000..1ef2c97c3
--- /dev/null
+++ b/test/integration/model/nested_include/wheel/model.config
@@ -0,0 +1,6 @@
+<?xml version="1.0"?>
+<model>
+  <name>wheel</name>
+  <sdf version="1.7">wheel.sdf</sdf>
+</model>
+
diff --git a/test/integration/model/nested_include/wheel/wheel.sdf b/test/integration/model/nested_include/wheel/wheel.sdf
new file mode 100644
index 000000000..7556007ce
--- /dev/null
+++ b/test/integration/model/nested_include/wheel/wheel.sdf
@@ -0,0 +1,38 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <model name="wheel">
+    <link name='wheel_link'>
+      <pose>0 0 0 0 0 0</pose>
+      <inertial>
+        <mass>2</mass>
+        <inertia>
+          <ixx>0.145833</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.145833</iyy>
+          <iyz>0</iyz>
+          <izz>0.125</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+        <material>
+          <ambient>0.2 0.2 0.2 1</ambient>
+          <diffuse>0.2 0.2 0.2 1</diffuse>
+          <specular>0.2 0.2 0.2 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+      </collision>
+    </link>
+  </model>
+</sdf>
diff --git a/test/integration/model/robot/model.config b/test/integration/model/robot/model.config
new file mode 100644
index 000000000..04a17df92
--- /dev/null
+++ b/test/integration/model/robot/model.config
@@ -0,0 +1,5 @@
+<?xml version="1.0"?>
+<model>
+  <name>robot</name>
+  <sdf version="1.7">model.sdf</sdf>
+</model>
diff --git a/test/integration/model/robot/model.sdf b/test/integration/model/robot/model.sdf
new file mode 100644
index 000000000..ec02e8359
--- /dev/null
+++ b/test/integration/model/robot/model.sdf
@@ -0,0 +1,315 @@
+<?xml version="1.0" ?>
+<sdf version="1.7">
+  <model name='vehicle'>
+    <pose>0 0 0.325 0 -0 0</pose>
+
+    <link name='chassis'>
+      <pose>-0.151427 -0 0.175 0 -0 0</pose>
+      <inertial>
+        <mass>1.14395</mass>
+        <inertia>
+          <ixx>0.126164</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.416519</iyy>
+          <iyz>0</iyz>
+          <izz>0.481014</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <box>
+            <size>2.01142 1 0.568726</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>0.5 0.5 1.0 1</ambient>
+          <diffuse>0.5 0.5 1.0 1</diffuse>
+          <specular>0.0 0.0 1.0 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <box>
+            <size>2.01142 1 0.568726</size>
+          </box>
+        </geometry>
+      </collision>
+
+      <visual name="lidar_visual">
+        <pose>-0.8 0 0.41 0 0 0</pose>
+          <geometry>
+              <cylinder>
+                  <radius>0.1</radius>
+                  <length>0.25</length>
+              </cylinder>
+          </geometry>
+      </visual>
+
+      <sensor name='lidar' type='gpu_lidar'>
+        <pose>-0.8 0 0.41 0 0 0</pose>
+        <topic>lidar</topic>
+        <update_rate>10</update_rate>
+        <lidar>
+          <scan>
+            <horizontal>
+              <samples>640</samples>
+              <resolution>1</resolution>
+              <min_angle>-1.396263</min_angle>
+              <max_angle>1.396263</max_angle>
+            </horizontal>
+            <vertical>
+              <samples>16</samples>
+              <resolution>1</resolution>
+              <min_angle>-0.261799</min_angle>
+              <max_angle>0.261799</max_angle>
+            </vertical>
+          </scan>
+          <range>
+            <min>0.08</min>
+            <max>10.0</max>
+            <resolution>0.01</resolution>
+          </range>
+        </lidar>
+        <alwaysOn>1</alwaysOn>
+        <visualize>true</visualize>
+      </sensor>
+
+      <sensor name="camera" type="camera">
+        <pose>-1.06 0 0 0 0 3.14</pose>
+        <camera>
+          <horizontal_fov>1.047</horizontal_fov>
+          <image>
+            <width>320</width>
+            <height>240</height>
+          </image>
+          <clip>
+            <near>0.1</near>
+            <far>100</far>
+          </clip>
+        </camera>
+        <always_on>1</always_on>
+        <visualize>true</visualize>
+        <update_rate>30</update_rate>
+        <topic>chassis/camera</topic>
+      </sensor>
+
+    </link>
+
+    <link name="top">
+      <pose>0.6 0 0.7 0 0 0</pose>
+      <collision name="top_collision">
+        <geometry>
+          <box>
+            <size>0.5 1 0.5</size>
+          </box>
+        </geometry>
+      </collision>
+      <visual name="top_visual">
+        <geometry>
+          <box>
+            <size>0.5 1 0.5</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>1 0 0 1</ambient>
+          <diffuse>1 0 0 1</diffuse>
+          <specular>1 0 0 1</specular>
+        </material>
+        <transparency>0.5</transparency>
+        <cast_shadows>1</cast_shadows>
+        <plugin name="top_plugin" filename="/path/to/plugin"/>
+        <plugin name="top_plugin2" filename="/path/to/plugin"/>
+        <plugin name="top_plugin3" filename="/path/to/plugin"/>
+      </visual>
+
+      <collision name="camera_collision">
+        <pose>-0.2 0 0.3 0 0 3.14</pose>
+        <geometry>
+          <box>
+            <size>0.1 0.1 0.1</size>
+          </box>
+        </geometry>
+      </collision>
+
+      <visual name="camera_visual">
+        <pose>-0.2 0 0.3 0 0 3.14</pose>
+        <geometry>
+          <box>
+            <size>0.1 0.1 0.1</size>
+          </box>
+        </geometry>
+        <material>
+          <ambient>0 1 0 1</ambient>
+          <diffuse>0 1 0 1</diffuse>
+          <specular>0.5 0.5 0.5 1</specular>
+          <lighting>1</lighting>
+        </material>
+        <plugin name='some_visual_plugin' filename='/path/to/plugin'/>
+      </visual>
+
+      <sensor name="camera" type="camera">
+        <pose>-0.2 0 0.3 0 0.0 0</pose>
+        <camera>
+          <horizontal_fov>2</horizontal_fov>
+          <image>
+            <width>320</width>
+            <height>240</height>
+          </image>
+          <clip>
+            <near>0.1</near>
+            <far>100</far>
+          </clip>
+        </camera>
+        <always_on>1</always_on>
+        <update_rate>30</update_rate>
+        <visualize>true</visualize>
+        <topic>top/camera</topic>
+      </sensor>
+
+    </link>
+
+    <joint name="top_to_base" type="fixed">
+      <parent>chassis</parent>
+      <child>top</child>
+    </joint>
+
+    <link name='left_wheel'>
+      <pose>0.554283 0.625029 -0.025 -1.5707 0 0</pose>
+      <inertial>
+        <mass>2</mass>
+        <inertia>
+          <ixx>0.145833</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.145833</iyy>
+          <iyz>0</iyz>
+          <izz>0.125</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+        <material>
+          <ambient>0.2 0.2 0.2 1</ambient>
+          <diffuse>0.2 0.2 0.2 1</diffuse>
+          <specular>0.2 0.2 0.2 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+      </collision>
+    </link>
+
+    <link name='right_wheel'>
+      <pose>0.554282 -0.625029 -0.025 -1.5707 0 0</pose>
+      <inertial>
+        <mass>2</mass>
+        <inertia>
+          <ixx>0.145833</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.145833</iyy>
+          <iyz>0</iyz>
+          <izz>0.125</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+        <material>
+          <ambient>0.2 0.2 0.2 1</ambient>
+          <diffuse>0.2 0.2 0.2 1</diffuse>
+          <specular>0.2 0.2 0.2 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <sphere>
+            <radius>0.3</radius>
+          </sphere>
+        </geometry>
+      </collision>
+    </link>
+
+    <link name='caster'>
+      <pose>-0.957138 -0 -0.125 0 -0 0</pose>
+      <inertial>
+        <mass>1</mass>
+        <inertia>
+          <ixx>0.1</ixx>
+          <ixy>0</ixy>
+          <ixz>0</ixz>
+          <iyy>0.1</iyy>
+          <iyz>0</iyz>
+          <izz>0.1</izz>
+        </inertia>
+      </inertial>
+      <visual name='visual'>
+        <geometry>
+          <sphere>
+            <radius>0.2</radius>
+          </sphere>
+        </geometry>
+        <material>
+          <ambient>0.2 0.2 0.2 1</ambient>
+          <diffuse>0.2 0.2 0.2 1</diffuse>
+          <specular>0.2 0.2 0.2 1</specular>
+        </material>
+      </visual>
+      <collision name='collision'>
+        <geometry>
+          <sphere>
+            <radius>0.2</radius>
+          </sphere>
+        </geometry>
+      </collision>
+    </link>
+
+    <joint name='left_wheel_joint' type='revolute'>
+      <parent>chassis</parent>
+      <child>left_wheel</child>
+      <axis>
+        <xyz>0 0 1</xyz>
+        <limit>
+          <lower>-1.79769e+308</lower>
+          <upper>1.79769e+308</upper>
+        </limit>
+      </axis>
+    </joint>
+
+    <joint name='right_wheel_joint' type='revolute'>
+      <parent>chassis</parent>
+      <child>right_wheel</child>
+      <axis>
+        <xyz>0 0 1</xyz>
+        <limit>
+          <lower>-1.79769e+308</lower>
+          <upper>1.79769e+308</upper>
+        </limit>
+      </axis>
+    </joint>
+
+    <joint name='caster_wheel' type='ball'>
+      <parent>chassis</parent>
+      <child>caster</child>
+    </joint>
+
+    <model name="nested_models">
+      <pose>0 0 0 0 0 0</pose>
+      <model name="model1">
+        <link name="link1"/>
+      </model>
+    </model>
+  </model>
+</sdf>
diff --git a/test/integration/param_passing.cc b/test/integration/param_passing.cc
new file mode 100644
index 000000000..44a40ed1e
--- /dev/null
+++ b/test/integration/param_passing.cc
@@ -0,0 +1,165 @@
+/*
+ * Copyright 2020 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+#include <string>
+#include <gtest/gtest.h>
+#include "sdf/Filesystem.hh"
+#include "sdf/Root.hh"
+#include "test_config.h"
+
+void PrintErrors(sdf::Errors &_errors)
+{
+  for (sdf::Error e : _errors)
+    std::cout << e.Message() << std::endl;
+}
+
+/////////////////////////////////////////////////
+TEST(ParamPassingTest, ExperimentalParamsTag)
+{
+  const std::string modelRootPath =
+    sdf::testing::TestFile("integration", "model");
+  sdf::setFindCallback(
+      [&](const std::string &_file)
+      {
+        return sdf::filesystem::append(modelRootPath, _file);
+      });
+
+  // checks normal <include> (w/o <experimental:params>)
+  std::string testFile =
+    sdf::testing::TestFile("integration", "include_model.sdf");
+  sdf::Root root;
+  sdf::Errors errors = root.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_TRUE(errors.empty());
+
+  // checks <include> containing <experimental:params> w/ correctly specified
+  // elements
+  testFile = sdf::testing::TestFile("integration", "include_custom_model.sdf");
+  errors = root.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_TRUE(errors.empty());
+
+  // compare with expected output
+  testFile = sdf::testing::TestFile("integration",
+                                    "include_custom_model_expected_output.sdf");
+  sdf::Root expectedRoot;
+  errors = expectedRoot.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_TRUE(errors.empty());
+  EXPECT_EQ(root.Element()->ToString(""), expectedRoot.Element()->ToString(""))
+        << "ACTUAL:\n" << root.Element()->ToString("\t")
+        << "\nEXPECTED:\n" << expectedRoot.Element()->ToString("\t");
+
+  // Expected errors
+  testFile = sdf::testing::TestFile("integration",
+                                    "include_invalid_custom_model.sdf");
+  errors = root.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_FALSE(errors.empty());
+  ASSERT_EQ(errors.size(), 29u);
+
+  int i = -1;
+  // missing element_id attribute
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  // element does not exist in included model
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // element already exists in included model
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::DUPLICATE_NAME);
+  // for add action, parent of specified element does not exist
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // missing name after double colons
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // missing action attribute
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  // incorrect schema (missing required attributes; in children of element_id)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  // not defined sdf element (in children of where element_id is defined)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  // not defined sdf element (where element_id is defined)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  // missing 'name' attribute where element_id is with action="add"
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  // 'name' attribute is empty (where element_id is with action="add")
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // incorrect schema (missing required attributes; where element_id defined)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  // invalid action
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // invalid child action
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // child element does not exist
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // child <box> (child of <geometry>) does not exist
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // child element (w/ name attribute) does not exist
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // child element does not exist (replace action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // missing 'name' attribute (replace action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  // invalid attribute (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // element missing (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // incorrect schema (missing required attributes; where element_id defined)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_MISSING);
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  // invalid attribute (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ATTRIBUTE_INVALID);
+  // element missing (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // element missing (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_MISSING);
+  // element has invalid value (modify action)
+  EXPECT_EQ(errors[++i].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+}
+
+/////////////////////////////////////////////////
+TEST(ParamPassingTest, NestedInclude)
+{
+  const std::string modelRootPath =
+    sdf::testing::TestFile("integration", "model", "nested_include");
+  sdf::setFindCallback(
+      [&](const std::string &_file)
+      {
+        return sdf::filesystem::append(modelRootPath, _file);
+      });
+
+  // checks correctly specified elements in <experimental:params>
+  // at top-level include, which has several nested includes
+  // e.g., When model A includes B and B includes C. The top-level A
+  //       <experimental:params> specifies elements of C
+  std::string testFile =
+    sdf::testing::TestFile("integration", "model",
+                           "nested_include", "test_nested_include.sdf");
+  sdf::Root root;
+  sdf::Errors errors = root.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_TRUE(errors.empty());
+
+  // compare with expected output
+  testFile = sdf::testing::TestFile("integration",
+                           "include_custom_nested_model_expected_output.sdf");
+  sdf::Root expectedRoot;
+  errors = expectedRoot.Load(testFile);
+  PrintErrors(errors);
+  EXPECT_TRUE(errors.empty());
+  EXPECT_EQ(root.Element()->ToString(""), expectedRoot.Element()->ToString(""))
+        << "ACTUAL:\n" << root.Element()->ToString("\t")
+        << "\nEXPECTED:\n" << expectedRoot.Element()->ToString("\t");
+}

From 01bb85f06ea3baa7715a2c5a71ac84d12e0fd81d Mon Sep 17 00:00:00 2001
From: "Addisu Z. Taddese" <addisu@openrobotics.org>
Date: Mon, 28 Jun 2021 21:45:09 -0500
Subject: [PATCH 4/8] Fix ABI break (#605)

This moves the recently added data member `explicitlySetInFile` to the
end of the `ElementPrivate` class

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>
---
 include/sdf/Element.hh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/sdf/Element.hh b/include/sdf/Element.hh
index 798f7828e..27f3cc239 100644
--- a/include/sdf/Element.hh
+++ b/include/sdf/Element.hh
@@ -489,9 +489,6 @@ namespace sdf
     /// \brief True if element is required
     public: std::string required;
 
-    /// \brief True if the element was set in the SDF file.
-    public: bool explicitlySetInFile;
-
     /// \brief Element description
     public: std::string description;
 
@@ -524,6 +521,9 @@ namespace sdf
 
     /// \brief Spec version that this was originally parsed from.
     public: std::string originalVersion;
+
+    /// \brief True if the element was set in the SDF file.
+    public: bool explicitlySetInFile;
   };
 
   ///////////////////////////////////////////////

From 18f908b67d2c408538dc10422c4ccf8b8d6f6103 Mon Sep 17 00:00:00 2001
From: Steve Peters <scpeters@openrobotics.org>
Date: Wed, 30 Jun 2021 17:10:29 -0700
Subject: [PATCH 5/8] Add ValidateGraphs methods to Model/World (sdf9) (#602)

The graph data is private, so expose methods for
checking that the graphs are valid.

* Add tests showing graph errors

Load an sdf::World or sdf::Model instead of an sdf::Root to
see the graph errors.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>
---
 include/sdf/Model.hh          |   6 ++
 include/sdf/World.hh          |   6 ++
 src/FrameSemantics.cc         |   2 +-
 src/Model.cc                  |  29 ++++++++
 src/Model_TEST.cc             |  11 +++
 src/World.cc                  |  29 ++++++++
 src/World_TEST.cc             |  11 +++
 test/integration/frame.cc     | 127 +++++++++++++++++++++++++++++++++-
 test/integration/model_dom.cc |   3 +
 test/integration/world_dom.cc |   2 +
 10 files changed, 223 insertions(+), 3 deletions(-)

diff --git a/include/sdf/Model.hh b/include/sdf/Model.hh
index cfa25454e..454eb99c3 100644
--- a/include/sdf/Model.hh
+++ b/include/sdf/Model.hh
@@ -74,6 +74,12 @@ namespace sdf
     /// an error code and message. An empty vector indicates no error.
     public: Errors Load(ElementPtr _sdf);
 
+    /// \brief Check that the FrameAttachedToGraph and PoseRelativeToGraph
+    /// are valid.
+    /// \return Errors, which is a vector of Error objects. Each Error includes
+    /// an error code and message. An empty vector indicates no error.
+    public: Errors ValidateGraphs() const;
+
     /// \brief Get the name of the model.
     /// The name of the model should be unique within the scope of a World.
     /// \return Name of the model.
diff --git a/include/sdf/World.hh b/include/sdf/World.hh
index 2f513eaaa..3e333a104 100644
--- a/include/sdf/World.hh
+++ b/include/sdf/World.hh
@@ -76,6 +76,12 @@ namespace sdf
     /// an error code and message. An empty vector indicates no error.
     public: Errors Load(ElementPtr _sdf);
 
+    /// \brief Check that the FrameAttachedToGraph and PoseRelativeToGraph
+    /// are valid.
+    /// \return Errors, which is a vector of Error objects. Each Error includes
+    /// an error code and message. An empty vector indicates no error.
+    public: Errors ValidateGraphs() const;
+
     /// \brief Get the name of the world.
     /// \return Name of the world.
     public: std::string Name() const;
diff --git a/src/FrameSemantics.cc b/src/FrameSemantics.cc
index 57a0fe30a..323303001 100644
--- a/src/FrameSemantics.cc
+++ b/src/FrameSemantics.cc
@@ -1346,7 +1346,7 @@ Errors resolveFrameAttachedToBody(
     {
       errors.push_back({ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR,
           "Graph has __model__ scope but sink vertex named [" +
-          sinkVertex.Name() + "] does not have FrameType LINK OR MODEL "
+          sinkVertex.Name() + "] does not have FrameType LINK or MODEL "
           "when starting from vertex with name [" + _vertexName + "]."});
       return errors;
     }
diff --git a/src/Model.cc b/src/Model.cc
index 03629a798..e7e1ce759 100644
--- a/src/Model.cc
+++ b/src/Model.cc
@@ -409,6 +409,35 @@ Errors Model::Load(ElementPtr _sdf)
   return errors;
 }
 
+/////////////////////////////////////////////////
+Errors Model::ValidateGraphs() const
+{
+  Errors errors;
+  if (!this->dataPtr->frameAttachedToGraph)
+  {
+    errors.push_back({ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR,
+        "FrameAttachedToGraph pointer is null."});
+  }
+  else
+  {
+    errors = validateFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph);
+  }
+
+  if (!this->dataPtr->poseGraph)
+  {
+    errors.push_back({ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR,
+        "PoseRelativeToGraph pointer is null."});
+  }
+  else
+  {
+    Errors poseErrors =
+        validatePoseRelativeToGraph(*this->dataPtr->poseGraph);
+    errors.insert(errors.end(), poseErrors.begin(), poseErrors.end());
+  }
+
+  return errors;
+}
+
 /////////////////////////////////////////////////
 std::string Model::Name() const
 {
diff --git a/src/Model_TEST.cc b/src/Model_TEST.cc
index 86584b4a5..7172d53e0 100644
--- a/src/Model_TEST.cc
+++ b/src/Model_TEST.cc
@@ -109,6 +109,17 @@ TEST(DOMModel, Construction)
     // expect errors when trying to resolve pose
     EXPECT_FALSE(semanticPose.Resolve(pose).empty());
   }
+
+  auto errors = model.ValidateGraphs();
+  EXPECT_EQ(2u, errors.size());
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph pointer is null"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph pointer is null"));
 }
 
 /////////////////////////////////////////////////
diff --git a/src/World.cc b/src/World.cc
index 38ac9c1b3..47342a460 100644
--- a/src/World.cc
+++ b/src/World.cc
@@ -386,6 +386,35 @@ Errors World::Load(sdf::ElementPtr _sdf)
   return errors;
 }
 
+/////////////////////////////////////////////////
+Errors World::ValidateGraphs() const
+{
+  Errors errors;
+  if (!this->dataPtr->frameAttachedToGraph)
+  {
+    errors.push_back({ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR,
+        "FrameAttachedToGraph pointer is null."});
+  }
+  else
+  {
+    errors = validateFrameAttachedToGraph(*this->dataPtr->frameAttachedToGraph);
+  }
+
+  if (!this->dataPtr->poseRelativeToGraph)
+  {
+    errors.push_back({ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR,
+        "PoseRelativeToGraph pointer is null."});
+  }
+  else
+  {
+    Errors poseErrors =
+        validatePoseRelativeToGraph(*this->dataPtr->poseRelativeToGraph);
+    errors.insert(errors.end(), poseErrors.begin(), poseErrors.end());
+  }
+
+  return errors;
+}
+
 /////////////////////////////////////////////////
 std::string World::Name() const
 {
diff --git a/src/World_TEST.cc b/src/World_TEST.cc
index eb608ae3e..ba9b52a31 100644
--- a/src/World_TEST.cc
+++ b/src/World_TEST.cc
@@ -53,6 +53,17 @@ TEST(DOMWorld, Construction)
   EXPECT_FALSE(world.FrameNameExists("default"));
 
   EXPECT_EQ(1u, world.PhysicsCount());
+
+  auto errors = world.ValidateGraphs();
+  EXPECT_EQ(2u, errors.size());
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph pointer is null"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph pointer is null"));
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/frame.cc b/test/integration/frame.cc
index 02542f232..52238aa14 100644
--- a/test/integration/frame.cc
+++ b/test/integration/frame.cc
@@ -510,7 +510,67 @@ TEST(DOMFrame, LoadModelFramesInvalidAttachedTo)
       "causing a graph cycle"));
   // errors[7]
   // errors[8]
-  // errors[9]
+  EXPECT_EQ(errors[9].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[9].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [F4]"));
+
+  // Try loading sdf::Model object
+  sdf::SDFPtr sdfParsed(new sdf::SDF());
+  sdf::init(sdfParsed);
+  ASSERT_TRUE(sdf::readFile(testFile, sdfParsed));
+
+  auto rootElem = sdfParsed->Root();
+  ASSERT_NE(nullptr, rootElem);
+  ASSERT_TRUE(rootElem->HasElement("model"));
+  auto modelElem = rootElem->GetElement("model");
+  ASSERT_NE(nullptr, modelElem);
+
+  // the first 10 errors from loading an sdf::Model match the first 10 errors
+  // from loading an sdf::Root
+  sdf::Model model;
+  auto modelLoadErrors = model.Load(modelElem);
+  ASSERT_EQ(10u, modelLoadErrors.size());
+  for (int i = 0; i < 10; ++i)
+  {
+    EXPECT_EQ(errors[i].Code(), modelLoadErrors[i].Code());
+    EXPECT_EQ(errors[i].Message(), modelLoadErrors[i].Message());
+  }
+
+  errors = model.ValidateGraphs();
+  EXPECT_EQ(6u, errors.size());
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error, Non-LINK vertex with name [F3] is "
+      "disconnected; it should have 1 outgoing edge in MODEL attached_to "
+      "graph.")) << errors[0];
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "Graph has __model__ scope but sink vertex named [F3] does not have "
+      "FrameType LINK or MODEL when starting from vertex with name [F3]"))
+      << errors[1];
+  EXPECT_EQ(errors[2].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[2].Message().find(
+      "cycle detected, already visited vertex [F4]")) << errors[2];
+  EXPECT_EQ(errors[3].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[3].Message().find(
+      "Vertex with name [F3] is disconnected; it should have "
+      "1 incoming edge in MODEL relative_to graph")) << errors[3];
+  EXPECT_EQ(errors[4].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[4].Message().find(
+      "frame with name [F3] is disconnected; its source vertex has name [F3], "
+      "but its source name should be __model__")) << errors[4];
+  EXPECT_EQ(errors[5].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[5].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [F4]")) << errors[5];
 }
 
 /////////////////////////////////////////////////
@@ -720,6 +780,7 @@ TEST(DOMFrame, LoadWorldFramesInvalidAttachedTo)
       "causing a graph cycle"));
   // errors[2]
   // errors[3]
+  // errors[4]
   EXPECT_EQ(errors[5].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_INVALID);
   EXPECT_NE(std::string::npos,
     errors[5].Message().find(
@@ -730,9 +791,71 @@ TEST(DOMFrame, LoadWorldFramesInvalidAttachedTo)
     errors[6].Message().find(
       "relative_to name[self_cycle] is identical to frame name[self_cycle], "
       "causing a graph cycle"));
-  // errors[6]
   // errors[7]
   // errors[8]
+  EXPECT_EQ(errors[9].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[9].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [self_cycle]"));
+  EXPECT_EQ(errors[10].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  EXPECT_NE(std::string::npos,
+    errors[10].Message().find(
+      "Failed to load a world"));
+
+  // Try loading sdf::World object
+  sdf::SDFPtr sdfParsed(new sdf::SDF());
+  sdf::init(sdfParsed);
+  ASSERT_TRUE(sdf::readFile(testFile, sdfParsed));
+
+  auto rootElem = sdfParsed->Root();
+  ASSERT_NE(nullptr, rootElem);
+  ASSERT_TRUE(rootElem->HasElement("world"));
+  auto worldElem = rootElem->GetElement("world");
+  ASSERT_NE(nullptr, worldElem);
+
+  // the first 10 errors from loading an sdf::World match the first 10 errors
+  // from loading an sdf::Root
+  sdf::World world;
+  auto worldLoadErrors = world.Load(worldElem);
+  ASSERT_EQ(10u, worldLoadErrors.size());
+  for (int i = 0; i < 10; ++i)
+  {
+    EXPECT_EQ(errors[i].Code(), worldLoadErrors[i].Code());
+    EXPECT_EQ(errors[i].Message(), worldLoadErrors[i].Message());
+  }
+
+  errors = world.ValidateGraphs();
+  EXPECT_EQ(6u, errors.size());
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error, FRAME vertices in WORLD attached_to graph "
+      "should have 1 outgoing edge"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "Graph has world scope but sink vertex named [F] does not have "
+      "FrameType WORLD or MODEL when starting from vertex with name [F]"));
+  EXPECT_EQ(errors[2].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[2].Message().find(
+      "cycle detected, already visited vertex [self_cycle]"));
+  EXPECT_EQ(errors[3].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[3].Message().find(
+      "MODEL / FRAME vertex with name [F] is disconnected; it should have "
+      "1 incoming edge in WORLD relative_to graph"));
+  EXPECT_EQ(errors[4].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[4].Message().find(
+      "frame with name [F] is disconnected; its source vertex has name [F], "
+      "but its source name should be world"));
+  EXPECT_EQ(errors[5].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[5].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [self_cycle]"));
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/model_dom.cc b/test/integration/model_dom.cc
index 713d4cab0..6bab729d4 100644
--- a/test/integration/model_dom.cc
+++ b/test/integration/model_dom.cc
@@ -144,6 +144,9 @@ TEST(DOMRoot, LoadDoublePendulum)
 
   EXPECT_TRUE(model->JointNameExists("upper_joint"));
   EXPECT_TRUE(model->JointNameExists("lower_joint"));
+
+  auto graphErrors = model->ValidateGraphs();
+  EXPECT_EQ(0u, graphErrors.size());
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/world_dom.cc b/test/integration/world_dom.cc
index a59c482ec..878a74f0b 100644
--- a/test/integration/world_dom.cc
+++ b/test/integration/world_dom.cc
@@ -102,6 +102,8 @@ TEST(DOMWorld, Load)
   EXPECT_EQ(world->Gravity(), ignition::math::Vector3d(1, 2, 3));
   EXPECT_EQ(world->MagneticField(), ignition::math::Vector3d(-1, 0.5, 10));
   EXPECT_EQ(testFile, world->Element()->FilePath());
+  auto graphErrors = world->ValidateGraphs();
+  EXPECT_EQ(0u, graphErrors.size());
 
   const sdf::Atmosphere *atmosphere = world->Atmosphere();
   ASSERT_NE(nullptr, atmosphere);

From fd84096c6920564acfae88ad13ce0e8a78c74c6f Mon Sep 17 00:00:00 2001
From: Steve Peters <scpeters@openrobotics.org>
Date: Wed, 30 Jun 2021 17:12:13 -0700
Subject: [PATCH 6/8] Add ValidateGraphs methods to Model/World (#601)

The graph data is private, so expose methods for
checking that the graphs are valid.

* Add tests showing graph errors

Load an sdf::World or sdf::Model instead of an sdf::Root to
see the graph errors.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>
---
 include/sdf/Model.hh          |  6 +++
 include/sdf/World.hh          |  6 +++
 src/FrameSemantics.cc         | 18 ++++++++-
 src/Model.cc                  | 11 ++++++
 src/Model_TEST.cc             | 13 +++++++
 src/World.cc                  | 11 ++++++
 src/World_TEST.cc             | 11 ++++++
 test/integration/frame.cc     | 73 ++++++++++++++++++++++++++++++++++-
 test/integration/model_dom.cc |  3 ++
 test/integration/world_dom.cc |  2 +
 10 files changed, 151 insertions(+), 3 deletions(-)

diff --git a/include/sdf/Model.hh b/include/sdf/Model.hh
index f9f3f83af..aa85a7b3e 100644
--- a/include/sdf/Model.hh
+++ b/include/sdf/Model.hh
@@ -67,6 +67,12 @@ namespace sdf
     /// an error code and message. An empty vector indicates no error.
     public: Errors Load(sdf::ElementPtr _sdf, const ParserConfig &_config);
 
+    /// \brief Check that the FrameAttachedToGraph and PoseRelativeToGraph
+    /// are valid.
+    /// \return Errors, which is a vector of Error objects. Each Error includes
+    /// an error code and message. An empty vector indicates no error.
+    public: Errors ValidateGraphs() const;
+
     /// \brief Get the name of the model.
     /// The name of the model should be unique within the scope of a World.
     /// \return Name of the model.
diff --git a/include/sdf/World.hh b/include/sdf/World.hh
index 82fa00c97..183e83e2e 100644
--- a/include/sdf/World.hh
+++ b/include/sdf/World.hh
@@ -70,6 +70,12 @@ namespace sdf
     /// an error code and message. An empty vector indicates no error.
     public: Errors Load(sdf::ElementPtr _sdf, const ParserConfig &_config);
 
+    /// \brief Check that the FrameAttachedToGraph and PoseRelativeToGraph
+    /// are valid.
+    /// \return Errors, which is a vector of Error objects. Each Error includes
+    /// an error code and message. An empty vector indicates no error.
+    public: Errors ValidateGraphs() const;
+
     /// \brief Get the name of the world.
     /// \return Name of the world.
     public: std::string Name() const;
diff --git a/src/FrameSemantics.cc b/src/FrameSemantics.cc
index 5b290e7af..496111f18 100644
--- a/src/FrameSemantics.cc
+++ b/src/FrameSemantics.cc
@@ -1611,6 +1611,14 @@ Errors validateFrameAttachedToGraph(
 {
   Errors errors;
 
+  // Check if scope points to a valid graph
+  if (!_in)
+  {
+    errors.push_back({ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR,
+        "FrameAttachedToGraph error: scope does not point to a valid graph."});
+    return errors;
+  }
+
   // Expect ScopeContextName to be either "__model__" or "world"
   if (_in.ScopeContextName() != "__model__" &&
       _in.ScopeContextName() != "world")
@@ -1837,6 +1845,14 @@ Errors validatePoseRelativeToGraph(
 {
   Errors errors;
 
+  // Check if scope points to a valid graph
+  if (!_in)
+  {
+    errors.push_back({ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR,
+        "PoseRelativeToGraph error: scope does not point to a valid graph."});
+    return errors;
+  }
+
   // Expect scopeContextName to be either "__model__" or "world"
   if (_in.ScopeContextName() != "__model__" &&
       _in.ScopeContextName() != "world")
@@ -2089,7 +2105,7 @@ Errors resolveFrameAttachedToBody(
     {
       errors.push_back({ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR,
           "Graph has __model__ scope but sink vertex named [" +
-          sinkVertex.Name() + "] does not have FrameType LINK OR STATIC_MODEL "
+          sinkVertex.Name() + "] does not have FrameType LINK or STATIC_MODEL "
           "when starting from vertex with name [" + _vertexName + "]."});
       return errors;
     }
diff --git a/src/Model.cc b/src/Model.cc
index 8d0bbe1e2..1aa981069 100644
--- a/src/Model.cc
+++ b/src/Model.cc
@@ -326,6 +326,17 @@ Errors Model::Load(sdf::ElementPtr _sdf, const ParserConfig &_config)
   return errors;
 }
 
+/////////////////////////////////////////////////
+Errors Model::ValidateGraphs() const
+{
+  Errors errors =
+      validateFrameAttachedToGraph(this->dataPtr->frameAttachedToGraph);
+  Errors poseErrors =
+      validatePoseRelativeToGraph(this->dataPtr->poseGraph);
+  errors.insert(errors.end(), poseErrors.begin(), poseErrors.end());
+  return errors;
+}
+
 /////////////////////////////////////////////////
 std::string Model::Name() const
 {
diff --git a/src/Model_TEST.cc b/src/Model_TEST.cc
index 837f100ba..06cc2e881 100644
--- a/src/Model_TEST.cc
+++ b/src/Model_TEST.cc
@@ -138,6 +138,19 @@ TEST(DOMModel, Construction)
     // expect errors when trying to resolve pose
     EXPECT_FALSE(semanticPose.Resolve(pose).empty());
   }
+
+  auto errors = model.ValidateGraphs();
+  EXPECT_EQ(2u, errors.size());
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error: scope does not point to a valid graph"))
+      << errors[0];
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph error: scope does not point to a valid graph"))
+      << errors[1];
 }
 
 /////////////////////////////////////////////////
diff --git a/src/World.cc b/src/World.cc
index bd0822076..d3041cb49 100644
--- a/src/World.cc
+++ b/src/World.cc
@@ -279,6 +279,17 @@ Errors World::Load(sdf::ElementPtr _sdf, const ParserConfig &_config)
   return errors;
 }
 
+/////////////////////////////////////////////////
+Errors World::ValidateGraphs() const
+{
+  Errors errors =
+      validateFrameAttachedToGraph(this->dataPtr->frameAttachedToGraph);
+  Errors poseErrors =
+      validatePoseRelativeToGraph(this->dataPtr->poseRelativeToGraph);
+  errors.insert(errors.end(), poseErrors.begin(), poseErrors.end());
+  return errors;
+}
+
 /////////////////////////////////////////////////
 std::string World::Name() const
 {
diff --git a/src/World_TEST.cc b/src/World_TEST.cc
index 987eed93e..f48e0eca2 100644
--- a/src/World_TEST.cc
+++ b/src/World_TEST.cc
@@ -59,6 +59,17 @@ TEST(DOMWorld, Construction)
   EXPECT_FALSE(world.FrameNameExists("default"));
 
   EXPECT_EQ(1u, world.PhysicsCount());
+
+  auto errors = world.ValidateGraphs();
+  EXPECT_EQ(2u, errors.size()) << errors;
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error: scope does not point to a valid graph"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph error: scope does not point to a valid graph"));
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/frame.cc b/test/integration/frame.cc
index 316f27ff3..c5ae76113 100644
--- a/test/integration/frame.cc
+++ b/test/integration/frame.cc
@@ -507,7 +507,39 @@ TEST(DOMFrame, LoadModelFramesInvalidAttachedTo)
       "causing a graph cycle"));
   // errors[7]
   // errors[8]
-  // errors[9]
+  EXPECT_EQ(errors[9].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[9].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [model_frame_invalid_attached_to::F4]"));
+
+  // Try loading sdf::Model object
+  sdf::SDFPtr sdfParsed(new sdf::SDF());
+  sdf::init(sdfParsed);
+  ASSERT_TRUE(sdf::readFile(testFile, sdfParsed));
+
+  auto rootElem = sdfParsed->Root();
+  ASSERT_NE(nullptr, rootElem);
+  ASSERT_TRUE(rootElem->HasElement("model"));
+  auto modelElem = rootElem->GetElement("model");
+  ASSERT_NE(nullptr, modelElem);
+
+  // there are no errors when loading an sdf::Model directly since it doesn't
+  // build graphs
+  sdf::Model model;
+  auto modelLoadErrors = model.Load(modelElem);
+  EXPECT_EQ(0u, modelLoadErrors.size()) << modelLoadErrors;
+
+  errors = model.ValidateGraphs();
+  ASSERT_EQ(2u, errors.size()) << errors;
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error: scope does not point to a valid graph"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph error: scope does not point to a valid graph"));
 }
 
 /////////////////////////////////////////////////
@@ -718,6 +750,7 @@ TEST(DOMFrame, LoadWorldFramesInvalidAttachedTo)
       "causing a graph cycle"));
   // errors[2]
   // errors[3]
+  // errors[4]
   EXPECT_EQ(errors[5].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_INVALID);
   EXPECT_NE(std::string::npos,
     errors[5].Message().find(
@@ -728,9 +761,45 @@ TEST(DOMFrame, LoadWorldFramesInvalidAttachedTo)
     errors[6].Message().find(
       "relative_to name[self_cycle] is identical to frame name[self_cycle], "
       "causing a graph cycle"));
-  // errors[6]
   // errors[7]
   // errors[8]
+  EXPECT_EQ(errors[9].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_CYCLE);
+  EXPECT_NE(std::string::npos,
+    errors[9].Message().find(
+      "PoseRelativeToGraph cycle detected, "
+      "already visited vertex [self_cycle]"));
+  EXPECT_EQ(errors[10].Code(), sdf::ErrorCode::ELEMENT_INVALID);
+  EXPECT_NE(std::string::npos,
+    errors[10].Message().find(
+      "Failed to load a world"));
+
+  // Try loading sdf::World object
+  sdf::SDFPtr sdfParsed(new sdf::SDF());
+  sdf::init(sdfParsed);
+  ASSERT_TRUE(sdf::readFile(testFile, sdfParsed));
+
+  auto rootElem = sdfParsed->Root();
+  ASSERT_NE(nullptr, rootElem);
+  ASSERT_TRUE(rootElem->HasElement("world"));
+  auto worldElem = rootElem->GetElement("world");
+  ASSERT_NE(nullptr, worldElem);
+
+  // there are no errors when loading an sdf::World directly since it doesn't
+  // build graphs
+  sdf::World world;
+  auto worldLoadErrors = world.Load(worldElem);
+  EXPECT_EQ(0u, worldLoadErrors.size()) << worldLoadErrors;
+
+  errors = world.ValidateGraphs();
+  ASSERT_EQ(2u, errors.size()) << errors;
+  EXPECT_EQ(errors[0].Code(), sdf::ErrorCode::FRAME_ATTACHED_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[0].Message().find(
+      "FrameAttachedToGraph error: scope does not point to a valid graph"));
+  EXPECT_EQ(errors[1].Code(), sdf::ErrorCode::POSE_RELATIVE_TO_GRAPH_ERROR);
+  EXPECT_NE(std::string::npos,
+    errors[1].Message().find(
+      "PoseRelativeToGraph error: scope does not point to a valid graph"));
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/model_dom.cc b/test/integration/model_dom.cc
index e8931eb0c..ff46d7ec6 100644
--- a/test/integration/model_dom.cc
+++ b/test/integration/model_dom.cc
@@ -140,6 +140,9 @@ TEST(DOMRoot, LoadDoublePendulum)
 
   EXPECT_TRUE(model->JointNameExists("upper_joint"));
   EXPECT_TRUE(model->JointNameExists("lower_joint"));
+
+  auto graphErrors = model->ValidateGraphs();
+  EXPECT_EQ(0u, graphErrors.size());
 }
 
 /////////////////////////////////////////////////
diff --git a/test/integration/world_dom.cc b/test/integration/world_dom.cc
index c119aa246..1e1aa1ab7 100644
--- a/test/integration/world_dom.cc
+++ b/test/integration/world_dom.cc
@@ -97,6 +97,8 @@ TEST(DOMWorld, Load)
   EXPECT_EQ(world->Gravity(), ignition::math::Vector3d(1, 2, 3));
   EXPECT_EQ(world->MagneticField(), ignition::math::Vector3d(-1, 0.5, 10));
   EXPECT_EQ(testFile, world->Element()->FilePath());
+  auto graphErrors = world->ValidateGraphs();
+  EXPECT_EQ(0u, graphErrors.size());
 
   const sdf::Atmosphere *atmosphere = world->Atmosphere();
   ASSERT_NE(nullptr, atmosphere);

From 4e9f2eb3244e1c218f9fe31284ecf92a93379bff Mon Sep 17 00:00:00 2001
From: "Addisu Z. Taddese" <addisu@openrobotics.org>
Date: Thu, 1 Jul 2021 17:10:42 -0500
Subject: [PATCH 7/8] =?UTF-8?q?=F0=9F=8E=88=2011.2.2=20(#616)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

* Prepare for 11.2.2

Signed-off-by: Steven Peters <scpeters@openrobotics.org>

Co-authored-by: Steve Peters <scpeters@openrobotics.org>
---
 CMakeLists.txt |  2 +-
 Changelog.md   | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8acbd36ea..368d9252a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,7 +28,7 @@ set (SDF_PROTOCOL_VERSION 1.8)
 
 set (SDF_MAJOR_VERSION 11)
 set (SDF_MINOR_VERSION 2)
-set (SDF_PATCH_VERSION 1)
+set (SDF_PATCH_VERSION 2)
 
 set (SDF_VERSION ${SDF_MAJOR_VERSION}.${SDF_MINOR_VERSION})
 set (SDF_VERSION_FULL ${SDF_MAJOR_VERSION}.${SDF_MINOR_VERSION}.${SDF_PATCH_VERSION})
diff --git a/Changelog.md b/Changelog.md
index 9dd94e68f..319a43a82 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -2,6 +2,17 @@
 
 ### libsdformat 11.X.X (202X-XX-XX)
 
+### libsdformat 11.2.2 (2021-07-01)
+
+1. Fix segfault when checking for required elements in joint
+    * [Pull request #610](https://github.com/ignitionrobotics/sdformat/pull/610)
+
+1. Add ValidateGraphs methods to Model/World
+    * [Pull request #601](https://github.com/ignitionrobotics/sdformat/pull/601)
+
+1. Making `PrintValues()` and `ToString()` able to not print default elements
+    * [Pull request #575](https://github.com/ignitionrobotics/sdformat/pull/575)
+
 ### libsdformat 11.2.1 (2021-06-28)
 
 1. Fix ABI break on sdf11

From cb6cd03eadcca179ab6a35e5d3da2d48a7250fa7 Mon Sep 17 00:00:00 2001
From: Steve Peters <scpeters@openrobotics.org>
Date: Tue, 13 Jul 2021 12:24:14 -0700
Subject: [PATCH 8/8] Error: move << operator from .hh to .cc file (#623)

* Error: move << operator from .hh to .cc file

Signed-off-by: Steven Peters <scpeters@openrobotics.org>

* Fix visibility

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Co-authored-by: Addisu Z. Taddese <addisu@openrobotics.org>
---
 include/sdf/Error.hh | 26 ++------------------------
 src/Error.cc         | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 24 deletions(-)

diff --git a/include/sdf/Error.hh b/include/sdf/Error.hh
index 5d8cfe101..420626109 100644
--- a/include/sdf/Error.hh
+++ b/include/sdf/Error.hh
@@ -221,30 +221,8 @@ namespace sdf
     /// \param[in,out] _out The output stream.
     /// \param[in] _err The error to output.
     /// \return Reference to the given output stream
-    public: friend std::ostream &operator<<(std::ostream &_out,
-                                            const sdf::Error &_err)
-    {
-      std::string pathInfo = "";
-
-      if (_err.XmlPath().has_value())
-        pathInfo += _err.XmlPath().value();
-
-      if (_err.FilePath().has_value())
-        pathInfo += ":" + _err.FilePath().value();
-
-      if (_err.LineNumber().has_value())
-        pathInfo += ":L" + std::to_string(_err.LineNumber().value());
-
-      if (!pathInfo.empty())
-        pathInfo = "[" + pathInfo + "]: ";
-
-      _out << "Error Code "
-          << static_cast<std::underlying_type<sdf::ErrorCode>::type>(
-              _err.Code()) << ": "
-          << pathInfo
-          << "Msg: " << _err.Message();
-      return _out;
-    }
+    public: friend SDFORMAT_VISIBLE std::ostream &operator<<(
+        std::ostream &_out, const sdf::Error &_err);
 
     /// \brief Private data pointer.
     IGN_UTILS_IMPL_PTR(dataPtr)
diff --git a/src/Error.cc b/src/Error.cc
index 578857c0c..de8ea66de 100644
--- a/src/Error.cc
+++ b/src/Error.cc
@@ -120,3 +120,36 @@ bool Error::operator==(const bool _value) const
   return ((this->dataPtr->code != ErrorCode::NONE) && _value) ||
          ((this->dataPtr->code == ErrorCode::NONE) && !_value);
 }
+
+namespace sdf
+{
+// Inline bracket to help doxygen filtering.
+inline namespace SDF_VERSION_NAMESPACE {
+
+/////////////////////////////////////////////////
+// cppcheck-suppress unusedFunction
+std::ostream &operator<<(std::ostream &_out, const sdf::Error &_err)
+{
+  std::string pathInfo = "";
+
+  if (_err.XmlPath().has_value())
+    pathInfo += _err.XmlPath().value();
+
+  if (_err.FilePath().has_value())
+    pathInfo += ":" + _err.FilePath().value();
+
+  if (_err.LineNumber().has_value())
+    pathInfo += ":L" + std::to_string(_err.LineNumber().value());
+
+  if (!pathInfo.empty())
+    pathInfo = "[" + pathInfo + "]: ";
+
+  _out << "Error Code "
+      << static_cast<std::underlying_type<sdf::ErrorCode>::type>(
+          _err.Code()) << ": "
+      << pathInfo
+      << "Msg: " << _err.Message();
+  return _out;
+}
+}
+}