[cssom] Make removing a rule or style sheet null the parents.

Author: Simon Pieters

cssom/Overview.src.html

@@ -987,7 +987,8 @@ <h3>CSS Style Sheet Collections</h3>
 <ol>
  <li><p>Remove the <span>CSS style sheet</span> from the list of <span>document CSS style sheets</span>.
 
- <li><p>Set the <span>CSS style sheet</span>'s <span title=concept-css-style-sheet-owner-node>owner node</span> to null.
+ <li><p>Set the <span>CSS style sheet</span>'s <span title=concept-css-style-sheet-parent-css-style-sheet>parent CSS style sheet</span>,
+ <span title=concept-css-style-sheet-owner-node>owner node</span> and <span title=concept-css-style-sheet-owner-css-rule>owner CSS rule</span> to null.
 
  <!-- "associated CSS style sheet" is defined in terms of owner node, so we don't need to set it to null explicitly -->
 
@@ -1621,24 +1622,23 @@ <h3>CSS Rules</h3>
 <dl>
 <dt><dfn title=concept-css-rule-type>type</dfn></dt>
 <dd><p>A non-negative integer associated with a particular type of rule.
-This item is initialized when a rule is created and must never change.</p></dd>
+This item is initialized when a rule is created and cannot change.</p></dd>
 
 <dt><dfn title=concept-css-rule-text>text</dfn></dt>
 <dd><p>A text representation of the rule suitable for direct use in a style sheet.
-This item is initialized when a rule is created, and may change over the lifetime of the rule.</p></dd>
+This item is initialized when a rule is created and can be changed.</p></dd>
 
 <dt><dfn title=concept-css-rule-parent-css-rule>parent CSS rule</dfn></dt>
 <dd><p>A reference to an enclosing <span>CSS rule</span> or null.
-If the rule has an enclosing rule when it is created, then this item is initialized to the enclosing rule; otherwise it is null.
-Subsequent to initialization, this item is reset to null if the rule becomes non-enclosed. Once reset to null, it must never change.</p></dd>
+If the rule has an enclosing rule when it is created, then this item is initialized to the enclosing rule; otherwise it is null. It can be changed to
+null.</p></dd>
 
 <dt><dfn title=concept-css-rule-parent-css-style-sheet>parent CSS style sheet</dfn></dt>
 <dd><p>A reference to a parent <span>CSS style sheet</span> or null.
-This item is initialized to reference an associated style sheet when the rule is created. Subsequent to initialization, this item
-is reset to null if the rule becomes disassociated from its initial style sheet. Once reset to null, it must never change.</p></dd>
+This item is initialized to reference an associated style sheet when the rule is created. It can be changed to null.</p></dd>
 
 <dt><dfn title=concept-css-rule-child-css-rules>child CSS rules</dfn>
-<dd><p>A list of child <span title="CSS rule">CSS rules</span>.
+<dd><p>A list of child <span title="CSS rule">CSS rules</span>. The list can be mutated.
 </dl>
 
 <p>In addition to the above state, each <span>CSS rule</span> may be associated
@@ -1745,6 +1745,8 @@ <h3>CSS Rules</h3>
  <code title>@charset</code> at-rules, <code title>@import</code> at-rules, and <code title>@namespace</code> at-rules,
  <span data-anolis-spec='dom' title='concept-throw'>throw</span> an <code data-anolis-spec=dom>InvalidStateError</code> exception.
  <li><p>Remove rule <var>old rule</var> from <var>list</var> at the zero-indexed position <var>index</var>.<p></li>
+ <li><p>Set <var>old rule</var>'s <span title=concept-css-rule-parent-css-rule>parent CSS rule</span> and
+ <span title=concept-css-rule-parent-css-style-sheet>parent CSS style sheet</span> to null.
 </ol>