Strictly enforce exclusive semantics for <details name>.

This change thoroughly enforces that at most one <details> element in a
group established by the name attribute is open at a given time.   This
requires that we remove the open attribute during insertion into the DOM
in some cases, and also that we remove the open attribute for some
mutations of the name attribute.

This suppresses DOM mutation events (but not toggle events, which are
asynchronous) for the removals of the open attribute that result from
insertion.

This is based on discussion in (among other places):
openui/open-ui#786
openui/open-ui#812

Bug: 1444057
Change-Id: I91313662f6fb005b461717445a69294bcb4d1a59

html/semantics/interactive-elements/the-details-element/name-attribute.tentative.html

@@ -75,9 +75,9 @@
     assert_array_equals([first.open, second.open, third.open], [expected_first, expected_second, expected_third], description);
   }
 
-  assert_states(true, false, true, "initial states from open attribute");
+  assert_states(true, false, false, "initial states from open attribute");
   first.open = true;
-  assert_states(true, false, true, "non-mutation doesn't change state");
+  assert_states(true, false, false, "non-mutation doesn't change state");
   second.open = true;
   assert_states(false, true, false, "mutation closes multiple open elements");
   third.setAttribute("open", "");
@@ -148,19 +148,19 @@
     }));
   }
   assert_array_equals(mutation_event_received_ids, []);
-  assert_element_states(elements, [1, 0, 1, 1], "states before mutation");
+  assert_element_states(elements, [1, 0, 0, 0], "states before mutation");
   elements[1].open = true;
   if (mutation_event_received_ids.length == 0) {
     // ok if mutation events are not supported
   } else {
-    assert_array_equals(mutation_event_received_ids, ["e0", "e2", "e3", "e1"],
-                        "removal events received in tree order, followed by addition event");
+    assert_array_equals(mutation_event_received_ids, ["e0", "e1"],
+                        "removal event followed by addition event");
   }
   assert_element_states(elements, [0, 1, 0, 0], "states after mutation");
   assert_array_equals(toggle_event_received_ids, [], "toggle events received before awaiting promises");
   await Promise.all(toggle_event_promises);
-  assert_array_equals(toggle_event_received_ids, ["e1", "e0", "e2", "e3"], "toggle events received after awaiting promises");
-}, "mutation event and toggle event order matches tree order");
+  assert_array_equals(toggle_event_received_ids, ["e3", "e2", "e1", "e0"], "toggle events received after awaiting promises, including toggle events from parser insertion");
+}, "mutation event and toggle event order");
 
 // This function is used to guard tests that test behavior that is
 // relevant only because of Mutation Events.  If mutation events (for
@@ -203,9 +203,9 @@
     element.addEventListener("DOMSubtreeModified", listener);
   }
   assert_array_equals(received_ids, []);
-  assert_element_states(elements, [1, 0, 1], "states before mutation");
+  assert_element_states(elements, [1, 0, 0], "states before mutation");
   elements[1].open = true;
-  assert_array_equals(received_ids, ["e0", "e2", "e1"],
+  assert_array_equals(received_ids, ["e0", "e1"],
                       "removal events received in tree order, followed by addition event, despite changes to name during mutation event");
   assert_element_states(elements, [0, 1, 0], "states after mutation");
 }, "interaction of open attribute changes with mutation events");
@@ -326,4 +326,38 @@
   }, `exclusivity enforcement with attachment scenario ${scenario}`);
 }
 
+promise_test(async t => {
+  container.innerHTML = `
+    <details name="a" id="e0" open></details>
+    <details name="a" id="e1"></details>
+    <details name="b" id="e2" open></details>
+  `;
+  let elements = [ document.getElementById("e0"),
+                   document.getElementById("e1"),
+                   document.getElementById("e2") ];
+
+  assert_element_states(elements, [1, 0, 1], "states before first mutation");
+  elements[2].name = "a";
+  assert_element_states(elements, [1, 0, 0], "states after first mutation");
+  elements[0].name = "c";
+  elements[2].open = true;
+  assert_element_states(elements, [1, 0, 1], "states before second mutation");
+  elements[0].name = "a";
+  assert_element_states(elements, [0, 0, 1], "states after second mutation");
+}, "handling of name attribute changes");
+
+promise_test(async t => {
+  container.innerHTML = `
+    <details name="a" id="e0" open></details>
+    <details name="a" id="e1" open></details>
+    <details open name="a" id="e2"></details>
+  `;
+  let elements = [ document.getElementById("e0"),
+                   document.getElementById("e1"),
+                   document.getElementById("e2") ];
+
+  assert_element_states(elements, [1, 0, 0], "states after insertion by parser");
+}, "closing as a result of parsing doesn't depend on attribute order");
+
+
 </script>