Updated aria-setsize and aria-posinset to clarify usage for authors (#1332)

MelSumner · carmacleod · mcking65 · web-flow · commit c908c7f9af64 · 2021-03-19T15:34:56.000-07:00
Co-authored-by: Carolyn MacLeod &lt;Carolyn_MacLeod@ca.ibm.com&gt;
Co-authored-by: Matt King &lt;a11yThinker@Gmail.com&gt;
diff --git a/index.html b/index.html
@@ -12425,8 +12425,8 @@ <h2>Definitions of States and Properties (all aria-* attributes)</h2>
   &lt;li role="option" aria-setsize="16" <strong>aria-posinset="7"</strong>&gt; cantaloupes &lt;/li&gt;
   &lt;li role="option" aria-setsize="16" <strong>aria-posinset="8"</strong>&gt; dates &lt;/li&gt;
 &lt;/ul&gt;</pre>
-				<p>Authors MUST set the value for <pref>aria-posinset</pref> to an integer greater than or equal to 1, and less than or equal to the size of the set when that size is known. Authors SHOULD use <pref>aria-setsize</pref>.</p>
-				<p>When exposing <code>aria-posinset</code> on a <rref>menuitem</rref>, <rref>menuitemcheckbox</rref>, or <rref>menuitemradio</rref>, authors SHOULD set the value of <code>aria-posinset</code> with respect to the total number of items in the <rref>menu</rref>, excluding any separators.</p>
+				<p>When specifying <pref>aria-posinset</pref>, authors MUST specify a value that is an integer greater than or equal to 1, and less than or equal to the size of the set when that size is known. If authors specify <pref>aria-posinset</pref>,  authors MUST also specify a value for <pref>aria-setsize</pref>.</p>
+				<p>When specifying <code>aria-posinset</code> on a <rref>menuitem</rref>, <rref>menuitemcheckbox</rref>, or <rref>menuitemradio</rref>, authors SHOULD set the value of <code>aria-posinset</code> with respect to the total number of items in the <rref>menu</rref>, excluding any separators.</p>
 			</div>
 			<table class="property-features">
 				<caption>Characteristics:</caption>
@@ -13061,9 +13061,9 @@ <h2>Definitions of States and Properties (all aria-* attributes)</h2>
 			<div class="property-description">
 				<p>Defines the number of items in the current set of listitems or treeitems. Not required if all elements in the set are present in the <abbr title="Document Object Model">DOM</abbr>. See related <pref>aria-posinset</pref>.</p>
 				<p>This <a>property</a> is marked on the members of a set, not the container element that collects the members of the set. To orient the user by saying an element is "item X out of Y," the <a>assistive technologies</a> would use X equal to the <pref>aria-posinset</pref> <a>attribute</a> and Y equal to the <code>aria-setsize</code> attribute.</p>
-				<p>If all items in a set are present in the document structure, it is not necessary to set this property, as the <a>user agent</a> can automatically calculate the set size and position for each item. However, if only a portion of the set is present in the document structure at a given moment (in order to reduce document size), this property is needed to provide an explicit indication of set size.</p>
-				<p>Authors MUST set the value of <code>aria-setsize</code> to an integer equal to the number of items in the set. If the total number of items is unknown, authors SHOULD set the value of <code>aria-setsize</code> to <code>-1</code>.</p>
-				<p>When exposing <code>aria-setsize</code> on a <rref>menuitem</rref>, <rref>menuitemcheckbox</rref>, or <rref>menuitemradio</rref>, authors SHOULD set the value of <code>aria-setsize</code> based on the total number of items in the <rref>menu</rref>, excluding any separators.</p>
+				<p>If all items up to the current item in a set are present in the document structure, it is not necessary to set this <a>attribute</a>, as the <a>user agent</a> can automatically calculate the position for these items. However, if all previous items in the set are not present in the document structure at a given moment, the author MUST set this <a>attribute</a>to provide an explicit indication of an element's position.</p>
+				<p>When specifying <code>aria-setsize</code>, authors MUST set the value to an integer equal to the number of items in the set. If the total number of items is unknown, authors SHOULD set the value of <code>aria-setsize</code> to <code>-1</code>.</p>
+				<p>When specifying <code>aria-setsize</code> on a <rref>menuitem</rref>, <rref>menuitemcheckbox</rref>, or <rref>menuitemradio</rref>, authors SHOULD set the value of <code>aria-setsize</code> based on the total number of items in the <rref>menu</rref>, excluding any separators.</p>
 				<p>The following example shows items 5 through 8 in a set of 16.</p>
 				<pre class="example highlight">&lt;h2 id="label_fruit"&gt; Available Fruit &lt;/h2&gt;
 &lt;ul role="listbox" aria-labelledby="label_fruit"&gt;
