Tweaks from zcorpan, squash into first commit

source

@@ -11788,7 +11788,7 @@ plaintext     = *( %x0000-2029 / %x202F-2065 / %x206A-10FFFF )
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
    <dd>A <code>head</code> element followed by a <code>body</code> element.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
-   <dd><span>Global attributes</span>, except the <code data-x="attr-is">is</code> attribute</dd>
+   <dd><span>Global attributes</span></dd>
    <dd><code data-x="attr-html-manifest">manifest</code></dd>
    <dt><span data-x="concept-element-dom">DOM interface</span>:</dt><!--TOPIC:DOM APIs-->
    <dd>
@@ -66582,7 +66582,7 @@ dictionary <dfn>ImageBitmapRenderingContextSettings</dfn> {
   data-x="element definition">defining</span> a custom element, authors can inform the parser how to
   properly construct an element and how elements of that class should react to changes.</p>
 
-  <p>Custom elements are part of a larger effort to "rationalise the platform," by explaining
+  <p>Custom elements are part of a larger effort to "rationalise the platform", by explaining
   existing platform features (like the elements of HTML) in terms of lower-level author-exposed
   extensibility points (like custom element definition). Although today there are many limitations
   on the capabilities of custom elements—both functionally and semantically—that prevent them from
@@ -66835,7 +66835,7 @@ console.log(plasticButton2.getAttribute("is")); // will output "plastic-button"<
   attributeChangedCallback() {
     // only is called for the disabled attribute due to observedAttributes
     if (this.disabled) {
-      this.setAttribute("tabindex", "-1");
+      this.removeAttribute("tabindex");
       this.setAttribute("aria-disabled", "true");
     } else {
       this.setAttribute("tabindex", "0");
@@ -67003,17 +67003,28 @@ console.log(plasticButton2.getAttribute("is")); // will output "plastic-button"<
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
    <dd><span>Transparent</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
-   <dd><span>Global attributes</span></dd>
+   <dd><span>Global attributes</span>, except the <code data-x="attr-is">is</code> attribute</dd>
    <dd>Any other attribute that has no namespace (see prose).</dd>
    <dt><span data-x="concept-element-dom">DOM interface</span>:</dt>
    <dd>Supplied by the element's author (inherits from <code>HTMLElement</code>)</dd>
   </dl>
 
   <p>An <span>autonomous custom element</span> does not have any special meaning: it
   <span>represents</span> its children. A <span>customized built-in element</span> inherits the
-  semantics of the element that it extends. Both types of <span>custom element</span> may have any
-  non-namespaced attributes that are relevant to the element's functioning, as determined by the
-  element's author.</p>
+  semantics of the element that it extends.</p>
+
+  <p>Any namespace-less attribute that is relevant to the element's functioning, as determined by
+  the element's author, may be specified on an <span>autonomous custom element</span>, so long as
+  the attribute name is <span>XML-compatible</span> and contains no <span>uppercase ASCII
+  letters</span>. The exception is the <code data-x="attr-is">is</code> attribute, which must not
+  be specified on an <span>autonomous custom element</span> (and which will have no effect if it
+  is).</p>
+
+  <p><span data-x="customized built-in element">Customized built-in elements</span> follow the
+  normal requirements for attributes, based on the elements they extend. To add custom
+  attribute-based behavior, use <code data-x="attr-data-*">data-*</code> attributes.</p>
+
+  <hr>
 
   <p>A <dfn data-export="">valid custom element name</dfn> is a sequence of characters
   <var>name</var> that meets all of the following requirements:</p>
@@ -67184,7 +67195,7 @@ dictionary <dfn>ElementRegistrationOptions</dfn> {
 
   <dl class="domintro">
    <dt><var>window</var> . <code data-x="dom-window-customElements">customElements</code> . <code
-   data-x="dom-CustomElementsRegistry-define">define</code>(<var>name</var>,
+   subdfn data-x="dom-CustomElementsRegistry-define">define</code>(<var>name</var>,
    <var>constructor</var>)</dt>
 
    <dd>Defines a new <span>custom element</span>, mapping the given name to the given constructor as
@@ -67201,7 +67212,7 @@ dictionary <dfn>ElementRegistrationOptions</dfn> {
    <span>custom element</span> or an unknown element.</dd>
 
    <dt><var>window</var> . <code data-x="dom-window-customElements">customElements</code> . <code
-   data-x="dom-CustomElementsRegistry-get">get</code>(<var>name</var>)</dt>
+   subdfn data-x="dom-CustomElementsRegistry-get">get</code>(<var>name</var>)</dt>
 
    <dd>Retrieves the <span>custom element constructor</span> defined for the given <span
    data-x="concept-custom-element-definition-name">name</span>. Returns undefined if there is no