Stricter language for authors using aria-owns (#1351)

* Stricter language for authors using aria-owns

Author: carmacleod

index.html

@@ -12270,7 +12270,8 @@ <h2>Definitions of States and Properties (all aria-* attributes)</h2>
 			<div class="property-description">
 				<p>Identifies an <a>element</a> (or elements) in order to define a visual, functional, or contextual parent/child <a>relationship</a> between <abbr title="Document Object Model">DOM</abbr> elements where the DOM hierarchy cannot be used to represent the relationship. See related <pref>aria-controls</pref>.</p>
 				<p>The value of the <pref>aria-owns</pref> <a>attribute</a> is a space-separated ID reference list that references one or more elements in the document by ID. The reason for adding <pref>aria-owns</pref> is to expose a parent/child contextual relationship to <a>assistive technologies</a> that is otherwise impossible to infer from the <abbr title="Document Object Model">DOM</abbr>.</p>
-				<p>If an element has both <pref>aria-owns</pref> and  <abbr title="Document Object Model">DOM</abbr> children then the order of the child elements with respect to the parent/child relationship is the <abbr title="Document Object Model">DOM</abbr> children first, then the elements referenced in <pref>aria-owns</pref>. If the author intends that the <abbr title="Document Object Model">DOM</abbr> children are not first, then list the DOM children in <pref>aria-owns</pref> in the desired order. Authors SHOULD NOT use <pref>aria-owns</pref> as a replacement for the <abbr title="Document Object Model">DOM</abbr> hierarchy. If the relationship is represented in the DOM, do not use <pref>aria-owns</pref>. Authors MUST ensure that an element's ID is not specified in more than one other element's <pref>aria-owns</pref> attribute at any time. In other words, an element can have only one explicit owner.</p>
+				<p>If an element has both <pref>aria-owns</pref> and  <abbr title="Document Object Model">DOM</abbr> children then the order of the child elements with respect to the parent/child relationship is the <abbr title="Document Object Model">DOM</abbr> children first, then the elements referenced in <pref>aria-owns</pref>. If the author intends that the <abbr title="Document Object Model">DOM</abbr> children are not first, then list the DOM children in <pref>aria-owns</pref> in the desired order. Authors SHOULD NOT use <pref>aria-owns</pref> as a replacement for the <abbr title="Document Object Model">DOM</abbr> hierarchy. If the relationship is represented in the DOM, do not use <pref>aria-owns</pref>.</p>
+				<p>Authors MUST ensure that an element's ID is not specified in more than one other element's <pref>aria-owns</pref> attribute at any time. In other words, an element can have only one explicit owner. Authors MUST NOT create circular references with <pref>aria-owns</pref>. In the case of authoring error with <pref>aria-owns</pref>, the user agent MAY ignore some <pref>aria-owns</pref> element references in order to build a consistent model of the content.</p>
 			</div>
 			<table class="property-features">
 				<caption>Characteristics:</caption>