diff --git a/docs/Traversal.md b/docs/Traversal.md
new file mode 100644
index 00000000..9c395889
--- /dev/null
+++ b/docs/Traversal.md
@@ -0,0 +1,92 @@
+
+# AST Traversal
+
+All Nodes implement the `IteratorAggregate` interface, which means their immediate children can be directly traversed with `foreach`:
+
+```php
+foreach ($node as $key => $child) {
+    var_dump($key)
+    var_dump($child);
+}
+```
+
+`$key` is set to the child name (e.g. `parameters`).
+Multiple child nodes may have the same key.
+
+The Iterator that is returned to `foreach` from `$node->getIterator()` implements the `RecursiveIterator` interface.
+To traverse all descendant nodes, you need to "flatten" it with PHP's built-in `RecursiveIteratorIterator`:
+
+```php
+$it = new \RecursiveIteratorIterator($node, \RecursiveIteratorIterator::SELF_FIRST);
+foreach ($it as $node) {
+    var_dump($node);
+}
+```
+
+The code above will walk all nodes and tokens depth-first.
+Passing `RecursiveIteratorIterator::CHILD_FIRST` would traverse breadth-first, while `RecursiveIteratorIterator::LEAVES_ONLY` (the default) would only traverse terminal Tokens. 
+
+## Exclude Tokens
+
+To exclude terminal Tokens and only traverse Nodes, use PHP's built-in `ParentIterator`:
+
+```php
+$nodes = new \ParentIterator(new \RecursiveIteratorIterator($node, \RecursiveIteratorIterator::SELF_FIRST));
+```
+
+## Skipping child traversal
+
+To skip traversal of certain Nodes, use PHP's `RecursiveCallbackIterator`.
+Naive example of traversing all nodes in the current scope:
+
+```php
+// Find all nodes in the current scope
+$nodesInScopeReIt = new \RecursiveCallbackFilterIterator($node, function ($current, string $key, \RecursiveIterator $it) {
+    // Don't traverse into function nodes, they form a different scope
+    return !($current instanceof Node\Expression\FunctionDeclaration);
+});
+// Convert the RecursiveIterator to a flat Iterator
+$it = new \RecursiveIteratorIterator($nodesInScope, \RecursiveIteratorIterator::SELF_FIRST);
+```
+
+## Filtering
+
+Building on that example, to get all variables in that scope us a non-recursive `CallbackFilterIterator`:
+
+```php
+// Filter out all variables
+$vars = new \CallbackFilterIterator($it, function ($current, string $key, \Iterator $it) {
+    return $current instanceof Node\Expression\Variable && $current->name instanceof Token;
+});
+
+foreach ($vars as $var) {
+    echo $var->name . PHP_EOL;
+}
+```
+
+## Traversing ancestors
+
+Use the `NodeAncestorIterator` to walk the AST upwards from a Node to the root.
+Example that finds the closest namespace Node to a Node:
+
+```php
+use Microsoft\PhpParser\Iterator\NodeAncestorIterator;
+use Microsoft\PhpParser\Node;
+
+foreach (new NodeAncestorIterator($node) as $ancestor) {
+    if ($ancestor instanceof Node\Statement\NamespaceDefinition) {
+        var_dump($ancestor->name);
+        break;
+    }
+}
+```
+
+## Converting to an array
+
+You can convert your iterator to a flat array with
+
+```php
+$arr = iterator_to_array($it, true);
+```
+
+The `true` ensures that the array is indexed numerically and not by Iterator keys (otherwise later Nodes with the same key will override previous Nodes).
diff --git a/docs/a.md b/docs/a.md
deleted file mode 100644
index e69de29b..00000000
diff --git a/phpunit.xml b/phpunit.xml
index 1812dacd..69114f79 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -35,6 +35,8 @@
       <file>tests/api/getResolvedName.php</file>
       <file>tests/api/PositionUtilitiesTest.php</file>
       <file>tests/api/TextEditTest.php</file>
+      <file>tests/api/NodeIteratorTest.php</file>
+      <file>tests/api/NodeAncestorIteratorTest.php</file>
     </testsuite>
 
     <testsuite name="performance">
diff --git a/src/Iterator/NodeAncestorIterator.php b/src/Iterator/NodeAncestorIterator.php
new file mode 100644
index 00000000..5f5c399f
--- /dev/null
+++ b/src/Iterator/NodeAncestorIterator.php
@@ -0,0 +1,75 @@
+<?php
+declare(strict_types = 1);
+
+namespace Microsoft\PhpParser\Iterator;
+
+use Microsoft\PhpParser\Node;
+
+/**
+ * An Iterator to walk the ancestors of a Node up to the root
+ */
+class NodeAncestorIterator implements \Iterator {
+
+    /**
+     * @var Node
+     */
+    private $start;
+
+    /**
+     * @var Node
+     */
+    private $current;
+
+    /**
+     * @param Node $node The node to start with
+     */
+    public function __construct(Node $node) {
+        $this->start = $node;
+    }
+
+    /**
+     * Rewinds the Iterator to the beginning
+     *
+     * @return void
+     */
+    public function rewind() {
+        $this->current = $this->start;
+    }
+
+    /**
+     * Returns `true` if `current()` can be called to get the current node.
+     * Returns `false` if the last Node was the root node.
+     *
+     * @return bool
+     */
+    public function valid() {
+        return $this->current !== null;
+    }
+
+    /**
+     * Always returns null.
+     *
+     * @return null
+     */
+    public function key() {
+        return null;
+    }
+
+    /**
+     * Returns the current Node
+     *
+     * @return Node
+     */
+    public function current() {
+        return $this->current;
+    }
+
+    /**
+     * Advances the Iterator to the parent of the current Node
+     *
+     * @return void
+     */
+    public function next() {
+        $this->current = $this->current->parent;
+    }
+}
diff --git a/src/Iterator/NodeIterator.php b/src/Iterator/NodeIterator.php
new file mode 100644
index 00000000..522c706f
--- /dev/null
+++ b/src/Iterator/NodeIterator.php
@@ -0,0 +1,161 @@
+<?php
+declare(strict_types = 1);
+
+namespace Microsoft\PhpParser\Iterator;
+
+use Microsoft\PhpParser\{Node, Token};
+
+/**
+ * An Iterator to the descendants of a Node
+ */
+class NodeIterator implements \RecursiveIterator {
+
+    /**
+     * The Node being iterated
+     *
+     * @var Node
+     */
+    private $node;
+
+    /**
+     * The current index in the CHILD_NAMES array
+     *
+     * @var int
+     */
+    private $childNamesIndex;
+
+    /**
+     * The length of the CHILD_NAMES array for the current node
+     *
+     * @var int
+     */
+    private $childNamesLength;
+
+    /**
+     * The current index of value at the current child name, if the value is an array.
+     * Otherwise null.
+     *
+     * @var int|null
+     */
+    private $valueIndex;
+
+    /**
+     * The length of the array at the current child name, if the value is an array.
+     * Otherwise null.
+     *
+     * @var int|null
+     */
+    private $valueLength;
+
+    private $childNames;
+
+    private $childName;
+
+    /**
+     * @param Node $node The node that should be iterated
+     */
+    public function __construct(Node $node) {
+        $this->node = $node;
+        $this->childNames = $node::CHILD_NAMES;
+        $this->childNamesLength = \count($node::CHILD_NAMES);
+    }
+
+    /**
+     * Rewinds the Iterator to the beginning
+     *
+     * @return void
+     */
+    public function rewind() {
+        $this->childNamesIndex = -1;
+        $this->next();
+    }
+
+    /**
+     * Returns `true` if `current()` can be called to get the current child.
+     * Returns `false` if this Node has no more children (direct descendants).
+     *
+     * @return bool
+     */
+    public function valid() {
+        return $this->childNamesIndex < $this->childNamesLength;
+    }
+
+    /**
+     * Returns the current child name being iterated.
+     * Multiple values may have the same key.
+     *
+     * @return string
+     */
+    public function key() {
+        return $this->childName;
+    }
+
+    /**
+     * Returns the current child (direct descendant)
+     *
+     * @return Node|Token
+     */
+    public function current() {
+        if ($this->valueIndex === null) {
+            return $this->node->{$this->childName};
+        } else {
+            return $this->node->{$this->childName}[$this->valueIndex];
+        }
+    }
+
+    /**
+     * Advances the Iterator to the next child (direct descendant)
+     *
+     * @return void
+     */
+    public function next() {
+        if ($this->valueIndex === $this->valueLength) {
+            // If not iterating value array or finished with it, go to next child name
+            $this->childNamesIndex++;
+            if ($this->childNamesIndex === $this->childNamesLength) {
+                // If child names index is invalid, become invalid
+                return;
+            }
+            $this->childName = $this->childNames[$this->childNamesIndex];
+            $value = $this->node->{$this->childName};
+            // If new value is null or empty array, skip it
+            if (empty($value)) {
+                $this->next();
+            } else if (\is_array($value)) {
+                // If new value is an array, start index at 0
+                $this->valueIndex = 0;
+                $this->valueLength = \count($value);
+            } else {
+                // Else reset everything to null
+                $this->valueIndex = null;
+                $this->valueLength = null;
+            }
+        } else {
+            // Else go to next item in value array
+            $this->valueIndex++;
+            // If new value is null or empty array, skip it
+            if (empty($this->node->{$this->childName}[$this->valueIndex])) {
+                $this->next();
+            }
+        }
+    }
+
+    /**
+     * Returns true if the current child is another Node (not a Token)
+     * and can be used to create another NodeIterator
+     *
+     * @return bool
+     */
+    public function hasChildren(): bool {
+        return $this->current() instanceof Node;
+    }
+
+    /**
+     * Returns a NodeIterator for the children of the current child Node
+     *
+     * @return NodeIterator
+     */
+    public function getChildren() {
+        return new NodeIterator($this->current());
+    }
+}
diff --git a/src/Node.php b/src/Node.php
index d6ddbe66..b4a721d1 100644
--- a/src/Node.php
+++ b/src/Node.php
@@ -12,7 +12,7 @@
 use Microsoft\PhpParser\Node\Statement\NamespaceDefinition;
 use Microsoft\PhpParser\Node\Statement\NamespaceUseDeclaration;
 
-abstract class Node implements \JsonSerializable {
+abstract class Node implements \JsonSerializable, \IteratorAggregate {
     /** @var array[] Map from node class to array of child keys */
     private static $childNames = [];
 
@@ -149,6 +149,15 @@ public function getRoot() : Node {
         return $node;
     }
 
+    /**
+     * Gets an Iterator to iterate all descendant nodes
+     *
+     * @return NodeIterator
+     */
+    public function getIterator() {
+        return new Iterator\NodeIterator($this);
+    }
+
     /**
      * Gets generator containing all descendant Nodes and Tokens.
      *
diff --git a/tests/api/NodeAncestorIteratorTest.php b/tests/api/NodeAncestorIteratorTest.php
new file mode 100644
index 00000000..91e1e6d8
--- /dev/null
+++ b/tests/api/NodeAncestorIteratorTest.php
@@ -0,0 +1,54 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Microsoft\PhpParser\{Parser, Node};
+use Microsoft\PhpParser\Iterator\NodeAncestorIterator;
+
+class NodeAncestorIteratorTest extends TestCase {
+    
+    const FILE_CONTENTS = '
+        <?php
+        function a() {
+            $a = 1;
+        }
+    ';
+
+    /** @var Node\SourceFileNode */
+    private $sourceFile;
+
+    public function setUp() {
+        $parser = new Parser();
+        $this->sourceFile = $parser->parseSourceFile(self::FILE_CONTENTS);
+    }
+
+    public function testIteratesAncestors() {
+        $it = new NodeAncestorIterator($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->leftOperand);
+        $it->rewind();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->leftOperand, $it->current());
+        $it->next();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression, $it->current());
+        $it->next();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0], $it->current());
+        $it->next();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon, $it->current());
+        $it->next();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile->statementList[1], $it->current());
+        $it->next();
+
+        $this->assertTrue($it->valid());
+        $this->assertSame($this->sourceFile, $it->current());
+        $it->next();
+
+        $this->assertFalse($it->valid());
+    }
+}
diff --git a/tests/api/NodeIteratorTest.php b/tests/api/NodeIteratorTest.php
new file mode 100644
index 00000000..5cf133e9
--- /dev/null
+++ b/tests/api/NodeIteratorTest.php
@@ -0,0 +1,186 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Microsoft\PhpParser\{Parser, Node};
+use Microsoft\PhpParser\Iterator\NodeIterator;
+
+class NodeIteratorTest extends TestCase {
+    
+    const FILE_CONTENTS = '
+        <?php
+        function a() {
+            $a = 1;
+        }
+    ';
+
+    /** @var Node\SourceFileNode */
+    private $sourceFile;
+
+    public function setUp() {
+        $parser = new Parser();
+        $this->sourceFile = $parser->parseSourceFile(self::FILE_CONTENTS);
+    }
+
+    public function testIteratesChildren() {
+        $it = new NodeIterator($this->sourceFile);
+        $it->rewind();
+
+        // Node\Statement\InlineHtml
+        $this->assertTrue($it->valid());
+        $this->assertSame('statementList', $it->key());
+        $this->assertSame($this->sourceFile->statementList[0], $it->current());
+        $it->next();
+
+        // Node\Statement\FunctionDeclaration
+        $this->assertTrue($it->valid());
+        $this->assertSame('statementList', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1], $it->current());
+        $it->next();
+
+        // Token(kind=EndOfFileToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('endOfFileToken', $it->key());
+        $this->assertSame($this->sourceFile->endOfFileToken, $it->current());
+        $it->next();
+
+        $this->assertFalse($it->valid());
+    }
+
+    public function testRecursiveIteratorIteratorIteratesDescendants() {
+        
+        $it = new \RecursiveIteratorIterator(new NodeIterator($this->sourceFile), \RecursiveIteratorIterator::SELF_FIRST);
+        $it->rewind();
+        
+        // Node\Statement\InlineHtml 
+        $this->assertTrue($it->valid());
+        $this->assertSame('statementList', $it->key());
+        $this->assertSame($this->sourceFile->statementList[0], $it->current());
+        $it->next();
+        
+        // Token(kind=InlineHtml)
+        $this->assertTrue($it->valid());
+        $this->assertSame('text', $it->key());
+        $this->assertSame($this->sourceFile->statementList[0]->text, $it->current());
+        $it->next();
+        
+        // <?php
+        // Token(kind=ScriptSectionStartTag)
+        $this->assertTrue($it->valid());
+        $this->assertSame('scriptSectionStartTag', $it->key());
+        $this->assertSame($this->sourceFile->statementList[0]->scriptSectionStartTag, $it->current());
+        $it->next();
+
+        // Node\Statement\FunctionDeclaration
+        $this->assertTrue($it->valid());
+        $this->assertSame('statementList', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1], $it->current());
+        $it->next();
+
+        // function
+        // Token(kind=FunctionKeyword)
+        $this->assertTrue($it->valid());
+        $this->assertSame('functionKeyword', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->functionKeyword, $it->current());
+        $it->next();
+
+        // a
+        // Token(kind=Name)
+        $this->assertTrue($it->valid());
+        $this->assertSame('name', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->name, $it->current());
+        $it->next();
+
+        // (
+        // Token(kind=OpenParenToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('openParen', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->openParen, $it->current());
+        $it->next();
+
+        // )
+        // Token(kind=CloseParenToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('closeParen', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->closeParen, $it->current());
+        $it->next();
+
+        // Node\Statement\CompoundStatementNode
+        $this->assertTrue($it->valid());
+        $this->assertSame('compoundStatementOrSemicolon', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon, $it->current());
+        $it->next();
+
+        // Node\Statement\CompoundStatementNode
+        $this->assertTrue($it->valid());
+        $this->assertSame('openBrace', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->openBrace, $it->current());
+        $it->next();
+
+        // Node\Statement\ExpressionStatement
+        $this->assertTrue($it->valid());
+        $this->assertSame('statements', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0], $it->current());
+        $it->next();
+
+        // Node\Expression\AssignmentExpression
+        $this->assertTrue($it->valid());
+        $this->assertSame('expression', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression, $it->current());
+        $it->next();
+
+        // Node\Expression\Variable
+        $this->assertTrue($it->valid());
+        $this->assertSame('leftOperand', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->leftOperand, $it->current());
+        $it->next();
+
+        // $a
+        // Token(kind=VariableName)
+        $this->assertTrue($it->valid());
+        $this->assertSame('name', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->leftOperand->name, $it->current());
+        $it->next();
+
+        // =
+        // Token(kind=EqualsToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('operator', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->operator, $it->current());
+        $it->next();
+
+        // Node\NumericLiteral
+        $this->assertTrue($it->valid());
+        $this->assertSame('rightOperand', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->rightOperand, $it->current());
+        $it->next();
+
+        // 1
+        // Token(kind=IntegerLiteralToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('children', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->expression->rightOperand->children, $it->current());
+        $it->next();
+
+        // ;
+        // Token(kind=SemicolonToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('semicolon', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->statements[0]->semicolon, $it->current());
+        $it->next();
+
+        // }
+        // Token(kind=CloseBraceToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('closeBrace', $it->key());
+        $this->assertSame($this->sourceFile->statementList[1]->compoundStatementOrSemicolon->closeBrace, $it->current());
+        $it->next();
+
+        // Token(kind=EndOfFileToken)
+        $this->assertTrue($it->valid());
+        $this->assertSame('endOfFileToken', $it->key());
+        $this->assertSame($this->sourceFile->endOfFileToken, $it->current());
+        $it->next();
+
+        $this->assertFalse($it->valid());
+    }
+}
diff --git a/validation/iteratorPerf1.php b/validation/iteratorPerf1.php
new file mode 100644
index 00000000..dabd0753
--- /dev/null
+++ b/validation/iteratorPerf1.php
@@ -0,0 +1,95 @@
+<?php
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+require_once(__DIR__ . "/../src/bootstrap.php");
+
+$totalSize = 0;
+$directoryIterator = new RecursiveDirectoryIterator(__DIR__ . "/frameworks/WordPress");
+$parser = new \Microsoft\PhpParser\Parser();
+$sourceFiles = array();
+
+foreach (new RecursiveIteratorIterator($directoryIterator) as $file) {
+    if (strpos($file, ".php")) {
+        $totalSize += $file->getSize();
+        $sourceFiles[] = $parser->parseSourceFile(file_get_contents($file->getPathname()));
+    }
+}
+
+$asts = [];
+
+$startMemory = memory_get_peak_usage(true);
+$startTime = microtime(true);
+
+function iterate($n) {
+    $i2 = 0;
+    foreach ($n::CHILD_NAMES as $name) {
+        $node = $n->$name;
+
+        if ($node === null) {
+            continue;
+        }
+
+        if (\is_array($node)) {
+            foreach ($node as $nodeArrItem) {
+                if ($nodeArrItem instanceof \Microsoft\PhpParser\Node) {   
+                    $i2++;
+                    $i2 += iterate($nodeArrItem);
+                }
+            }
+        } else if ($node instanceof \Microsoft\PhpParser\Node) {
+            $i2++;
+            $i2 += iterate($node);
+        } else {
+            $i2++;
+        }
+    }
+
+    return $i2;
+}
+
+$i = 0;
+foreach ($sourceFiles as $idx=>$sourceFile) {
+    $i += iterate($sourceFile);
+    $asts[] = $sourceFile;
+
+    if ($idx % 10 === 0) {
+        echo $idx;
+    }
+    if ($idx > 100) {
+        break;
+    }
+}
+
+echo PHP_EOL . "Total nodes: $i" . PHP_EOL;
+
+if (!isset($idx)) {
+    exit("Validation directory does not exist. First run `git submodule update --init --recursive from project root.`");
+}
+
+$asts = SplFixedArray::fromArray($asts);
+
+$endTime = microtime(true);
+$endMemory = memory_get_peak_usage(true);
+
+// TODO - multiple runs, calculate statistical significance
+$memoryUsage = $endMemory - $startMemory;
+$timeUsage = $endTime - $startTime;
+$totalSize /= 1024*1024;
+$memoryUsage /= 1024*1024;
+
+echo "MACHINE INFO\n";
+echo "============\n";
+echo "PHP int size: " . PHP_INT_SIZE . PHP_EOL;
+echo "PHP version: " . phpversion() . PHP_EOL;
+echo "OS: " . php_uname() . PHP_EOL . PHP_EOL;
+
+echo "PERF STATS\n";
+echo "==========\n";
+echo "Input Source Files (#): $idx\n";
+echo "Input Source Size (MB): $totalSize\n";
+echo PHP_EOL;
+echo "Time Usage (seconds): $timeUsage\n";
+echo "Memory Usage (MB): $memoryUsage\n";
diff --git a/validation/iteratorPerf2.php b/validation/iteratorPerf2.php
new file mode 100644
index 00000000..72e34c85
--- /dev/null
+++ b/validation/iteratorPerf2.php
@@ -0,0 +1,82 @@
+<?php
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+require_once(__DIR__ . "/../src/bootstrap.php");
+
+$totalSize = 0;
+$directoryIterator = new RecursiveDirectoryIterator(__DIR__ . "/frameworks/WordPress");
+$sourceFiles = array();
+$parser = new \Microsoft\PhpParser\Parser();
+
+foreach (new RecursiveIteratorIterator($directoryIterator) as $file) {
+    if (strpos($file, ".php")) {
+        $totalSize += $file->getSize();
+        $sourceFiles[] = $parser->parseSourceFile(file_get_contents($file->getPathname()));
+    }
+}
+
+$asts = [];
+
+$startMemory = memory_get_peak_usage(true);
+$startTime = microtime(true);
+
+
+function iterate($n) {
+    // Pass a callback to simulate filtering
+    $cb = function ($n) {
+        return true;
+    };
+    $i = 0;
+    foreach ($n->getDescendantNodesAndTokens($cb) as $child) {
+        $i++;
+    }
+
+    return $i;
+}
+
+$i = 0;
+foreach ($sourceFiles as $idx => $sourceFile) {
+    $i += iterate($sourceFile);
+    $asts[] = $sourceFile;
+
+    if ($idx % 10 === 0) {
+        echo $idx;
+    }
+    if ($idx > 100) {
+        break;
+    }
+}
+
+echo PHP_EOL . "Total nodes and tokens: $i" . PHP_EOL;
+
+if (!isset($idx)) {
+    exit("Validation directory does not exist. First run `git submodule update --init --recursive from project root.`");
+}
+
+$asts = SplFixedArray::fromArray($asts);
+
+$endTime = microtime(true);
+$endMemory = memory_get_peak_usage(true);
+
+// TODO - multiple runs, calculate statistical significance
+$memoryUsage = $endMemory - $startMemory;
+$timeUsage = $endTime - $startTime;
+$totalSize /= 1024*1024;
+$memoryUsage /= 1024*1024;
+
+echo "MACHINE INFO\n";
+echo "============\n";
+echo "PHP int size: " . PHP_INT_SIZE . PHP_EOL;
+echo "PHP version: " . phpversion() . PHP_EOL;
+echo "OS: " . php_uname() . PHP_EOL . PHP_EOL;
+
+echo "PERF STATS\n";
+echo "==========\n";
+echo "Input Source Files (#): $idx\n";
+echo "Input Source Size (MB): $totalSize\n";
+echo PHP_EOL;
+echo "Time Usage (seconds): $timeUsage\n";
+echo "Memory Usage (MB): $memoryUsage\n";
diff --git a/validation/iteratorPerf3.php b/validation/iteratorPerf3.php
new file mode 100644
index 00000000..17add021
--- /dev/null
+++ b/validation/iteratorPerf3.php
@@ -0,0 +1,80 @@
+<?php
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+require_once(__DIR__ . "/../src/bootstrap.php");
+
+use Microsoft\PhpParser\Iterator\NodeIterator;
+
+$totalSize = 0;
+$directoryIterator = new RecursiveDirectoryIterator(__DIR__ . "/frameworks/WordPress");
+$parser = new \Microsoft\PhpParser\Parser();
+$sourceFiles = array();
+
+foreach (new RecursiveIteratorIterator($directoryIterator) as $file) {
+    if (strpos($file, ".php")) {
+        $totalSize += $file->getSize();
+        $sourceFiles[] = $parser->parseSourceFile(file_get_contents($file->getPathname()));
+    }
+}
+
+$asts = [];
+
+$startMemory = memory_get_peak_usage(true);
+$startTime = microtime(true);
+
+function iterate($node) {
+    $i = 0;
+    $it = new \RecursiveIteratorIterator($node, \RecursiveIteratorIterator::SELF_FIRST);
+    foreach ($it as $node) {
+        $i++;
+    }
+
+    return $i;
+}
+
+$i = 0;
+foreach ($sourceFiles as $idx=>$sourceFile) {
+    $i += iterate($sourceFile);
+    $asts[] = $sourceFile;
+
+    if ($idx % 10 === 0) {
+        echo $idx;
+    }
+    if ($idx > 100) {
+        break;
+    }
+}
+
+echo PHP_EOL . "Total nodes: $i" . PHP_EOL;
+
+if (!isset($idx)) {
+    exit("Validation directory does not exist. First run `git submodule update --init --recursive from project root.`");
+}
+
+$asts = SplFixedArray::fromArray($asts);
+
+$endTime = microtime(true);
+$endMemory = memory_get_peak_usage(true);
+
+// TODO - multiple runs, calculate statistical significance
+$memoryUsage = $endMemory - $startMemory;
+$timeUsage = $endTime - $startTime;
+$totalSize /= 1024*1024;
+$memoryUsage /= 1024*1024;
+
+echo "MACHINE INFO\n";
+echo "============\n";
+echo "PHP int size: " . PHP_INT_SIZE . PHP_EOL;
+echo "PHP version: " . phpversion() . PHP_EOL;
+echo "OS: " . php_uname() . PHP_EOL . PHP_EOL;
+
+echo "PERF STATS\n";
+echo "==========\n";
+echo "Input Source Files (#): $idx\n";
+echo "Input Source Size (MB): $totalSize\n";
+echo PHP_EOL;
+echo "Time Usage (seconds): $timeUsage\n";
+echo "Memory Usage (MB): $memoryUsage\n";