Update content model for customizable select

This PR updated the content model for the <select>, <option>, and
<optgroup> elements in support of customizable <select>.

Fixes #10317

source

@@ -12785,6 +12785,34 @@ https://software.hixie.ch/utilities/js/live-dom-viewer/?%3C%21DOCTYPE%20HTML%3E%
   </ul>
 
 
+  <h6>Select element inner content elements</h6>
+
+  <p><dfn>Select element inner content elements</dfn> are <code>option</code> elements and other
+  elements which are used to group and decorate them with a <code>select</code> element.</p>
+
+  <p>The following are <span>select element inner content elements</span>:</p>
+
+  <ul class="brief category-list">
+   <li><code>option</code> elements.</li>
+
+   <li><code>optgroup</code> elements.</li>
+
+   <li><code>hr</code> elements.</li>
+
+   <li><span>script-supporting elements</span>.</li>
+
+   <li><code>noscript</code> elements.</li>
+
+   <li><code>div</code> elements.</li>
+
+   <li><code>span</code> elements.</li>
+
+   <li><code>img</code> elements.</li>
+
+   <li><span>SVG <code>svg</code></span> elements.</li>
+  </ul>
+
+
 
   <h5>Transparent content models</h5>
 
@@ -53203,7 +53231,8 @@ interface <dfn interface>HTMLButtonElement</dfn> : <span>HTMLElement</span> {
    <dt><span data-x="concept-element-contexts">Contexts in which this element can be used</span>:</dt>
    <dd>Where <span>phrasing content</span> is expected.</dd>
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
-   <dd>Zero or more <code>option</code>, <code>optgroup</code>, <code>hr</code>, and <span data-x="script-supporting elements">script-supporting</span> elements.</dd>
+   <dd>Zero or more <span>select element inner content elements</span>.</dd>
+   <dd>Zero or one child <code>button</code>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
    <dd><span>Global attributes</span></dd>
    <dd><code data-x="attr-fe-autocomplete">autocomplete</code></dd>
@@ -53932,9 +53961,9 @@ interface <dfn interface>HTMLDataListElement</dfn> : <span>HTMLElement</span> {
    <dt><span data-x="concept-element-categories">Categories</span>:</dt>
    <dd>None.</dd>
    <dt><span data-x="concept-element-contexts">Contexts in which this element can be used</span>:</dt>
-   <dd>As a child of a <code>select</code> element.</dd>
+   <dd>As a descendant of a <code>select</code> element.</dd>
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
-   <dd>Zero or more <code>option</code> and <span data-x="script-supporting elements">script-supporting</span> elements.</dd>
+   <dd>Zero or more <span>select element inner content elements</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
    <dd><span>Global attributes</span></dd>
    <dd><code data-x="attr-optgroup-disabled">disabled</code></dd>
@@ -54029,17 +54058,15 @@ interface <dfn interface>HTMLOptGroupElement</dfn> : <span>HTMLElement</span> {
    <dt><span data-x="concept-element-categories">Categories</span>:</dt>
    <dd>None.</dd>
    <dt><span data-x="concept-element-contexts">Contexts in which this element can be used</span>:</dt>
-   <dd>As a child of a <code>select</code> element.</dd>
+   <dd>As a descendant of a <code>select</code> element.</dd>
    <dd>As a child of a <code>datalist</code> element.</dd>
-   <dd>As a child of an <code>optgroup</code> element.</dd>
+   <dd>As a descendant of an <code>optgroup</code> element.</dd>
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
    <dd>If the element has a <code data-x="attr-option-label">label</code> attribute and a <code data-x="attr-option-value">value</code> attribute: <span data-x="concept-content-nothing">Nothing</span>.</dd>
    <dd>If the element has a <code data-x="attr-option-label">label</code> attribute but no <code data-x="attr-option-value">value</code> attribute: <span data-x="text content">Text</span>.</dd>
-   <dd>If the element has no <code data-x="attr-option-label">label</code> attribute and is not a
-   child of a <code>datalist</code> element: <span data-x="text content">Text</span> that is not
-   <span>inter-element whitespace</span>.</dd>
-   <dd>If the element has no <code data-x="attr-option-label">label</code> attribute and is a child
-   of a <code>datalist</code> element: <span data-x="text content">Text</span>.</dd>
+   <dd>If the element has no <code data-x="attr-option-label">label</code> attribute: <span>Text content</span> and zero or more <code>div</code>, <code>span</code>, <code>noscript</code>, <code>img</code>, <span>SVG <code>svg</code></span>, and <span data-x="script-supporting elements">script-supporting</span> elements.</dd>
+   <dd><div class="note">If an <code>img</code> is used within an <code>option</code> and there is no other text within the <code>option</code>, then the <code>option</code> won't have an accessible name unless the <code>img</code> also has a non-empty <code data-x="attr-img-alt">alt</code> attribute.</div></dd>
+
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
    <dd><span>Global attributes</span></dd>
    <dd><code data-x="attr-option-disabled">disabled</code></dd>