Make TextCluster an opaque object

source

@@ -65632,6 +65632,7 @@ interface <dfn interface>TextMetrics</dfn> {
 
 [Exposed=(Window,Worker)]
 interface <dfn interface>TextCluster</dfn> {
+    // opaque object
     readonly attribute double <span data-x="dom-TextCluster-x">x</span>;
     readonly attribute double <span data-x="dom-TextCluster-y">y</span>;
     readonly attribute unsigned long <span data-x="dom-TextCluster-begin">begin</span>;
@@ -69257,10 +69258,9 @@ try {
   <ol>
     <li><p>If any of the arguments are infinite or NaN, then return.</p></li>
 
-    <li><p>Run the <span>text preparation algorithm</span>, passing it the <var>text</var>
-    originally passed to <code data-x="dom-context-2d-measureText">measureText()</code> to obtain
-    the cluster, and an object with the <code>CanvasTextDrawingStyles</code> values as they were
-    when the cluster was measured, with the exception of <code
+    <li><p>Run the <span>text preparation algorithm</span>, passing it the complete text and the
+    <code>CanvasTextDrawingStyles</code> from the opaque <code>TextCluster</code>
+    <var>cluster</var>, with the exception of <code
     data-x="dom-context-2d-textAlign">textAlign</code> and <code
     data-x="dom-context-2d-textBaseline">textBaseline</code>, which are taken from the <code
     data-x="dom-TextCluster-align">align</code> and <code
@@ -69489,8 +69489,14 @@ try {
     <p>Splits the given range of the text into <span
     data-x="grapheme cluster">grapheme clusters</span>, and returns the positional data for each
     cluster. The range includes the character at the <var>start</var> index but stops before the
-    <var>end</var> index. The result is a list of new <code>TextCluster</code> objects with members
-    behaving as described in the following list: <ref>UNICODE</ref></p>
+    <var>end</var> index. The result is a list of new <code>TextCluster</code> objects. These
+    objects are opaque as they encapsulate the complete text that was segmented, along with the
+    <code>CanvasTextDrawingStyles</code> values that were active at the time <code
+    data-x="dom-context-2d-measureText">measureText()</code> was called. Note that <code
+    data-x="dom-context-2d-textAlign">textAlign</code> and
+    <code data-x="dom-context-2d-textBaseline">textBaseline</code> are exceptions, as they are explicitly set attributes and are handled separately. Each
+    <code>TextCluster</code> object has members behaving as described in the following list:
+    <ref>UNICODE</ref></p>
 
     <dl>
       <dt><dfn attribute for="TextCluster"><code data-x="dom-TextCluster-x">x</code></dfn> attribute</dt>
@@ -69555,11 +69561,6 @@ try {
       that this doesn't change the origin of the coordinate system, just which point is specified
       for each cluster.</p></dd>
     </dl>
-
-    <p class="note">The user agent might internally store in the <code>TextCluster</code> object the
-    complete text, as well as all the <code>CanvasTextDrawingStyles</code> at the time that <code
-    data-x="dom-context-2d-measureText">measureText()</code> was called, as they will be needed to
-    correctly render the clusters as they were measured.</p>
   </dd>
   </dl>