Introduce an explicit empty value default state

This replaces the use of the empty string as a keyword.

Fixes #11451.

Author: lukewarlow

source

@@ -5187,17 +5187,13 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
 
   <p>Some attributes, called <dfn data-x="enumerated attribute" data-lt="enumerated attribute"
   export>enumerated attributes</dfn>, take on a finite set of states. The state for such an
-  attribute is derived by combining the attribute's value, a set of keyword/state mappings given in
-  the specification of each attribute, and two possible special states that can also be given in the
-  specification of the attribute. These special states are the <dfn><i>invalid value
-  default</i></dfn> and the <dfn><i>missing value default</i></dfn>.</p>
+  attribute is derived by combining the attribute's value, a set of keyword/state mappings, and
+  three possible special states that can also be given in the specification of the attribute. These
+  special states are the <dfn><i>invalid value default</i></dfn>, the <dfn><i>missing value
+  default</i></dfn>, and the <dfn><i>empty value default</i></dfn>.</p>
 
   <p class="note">Multiple keywords can map to the same state.</p>
 
-  <p class="note">The empty string can be a valid keyword. Note that the <i data-x="missing value
-  default">missing value default</i> applies only when the attribute is <em>missing</em>, not when
-  it is present with an empty string value.</p>
-
   <p>To determine the state of an attribute, use the following steps:</p>
 
   <ol>
@@ -5216,6 +5212,10 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
    <li><p>If the attribute's value is an <span>ASCII case-insensitive</span> match for one of the
    keywords defined for the attribute, then return the state represented by that keyword.</p></li>
 
+   <li><p>If the attribute has an <i data-x="empty value default">empty value default</i> state
+   defined and the attribute's value is the empty string, then return that <i data-x="empty value
+   default">empty value default</i> state.</p></li>
+
    <li><p>If the attribute has an <i data-x="invalid value default">invalid value default</i> state
    defined, then return that <i data-x="invalid value default">invalid value default</i>
    state.</p></li>
@@ -5224,8 +5224,14 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   </ol>
 
   <p>For authoring conformance purposes, if an enumerated attribute is specified, the attribute's
-  value must be an <span>ASCII case-insensitive</span> match for one of the conforming keywords for
-  that attribute, with no leading or trailing whitespace.</p>
+  value must be one of:</p>
+
+  <ul>
+   <li><p>An <span>ASCII case-insensitive</span> match for one of the conforming keywords for that
+   attribute, with no leading or trailing whitespace.</p></li>
+   <li><p>The empty string and the attribute must have an <i data-x="empty value default">empty
+   value default</i> defined.</p></li>
+  </ul>
 
   <p>For <span data-x="reflect">reflection</span> purposes, states which have any keywords mapping
   to them are said to have a <dfn>canonical keyword</dfn>. This is determined as follows:</p>
@@ -7625,13 +7631,11 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
    <tbody>
     <tr>
      <td><dfn attr-value for="audio/crossorigin,video/crossorigin,img/crossorigin,link/crossorigin,script/crossorigin"><code data-x="attr-crossorigin-anonymous-keyword">anonymous</code></dfn>
-     <td rowspan=2><dfn data-x="attr-crossorigin-anonymous">Anonymous</dfn>
-     <td rowspan=2><span data-x="concept-request">Requests</span> for the element will have their
+     <td><dfn data-x="attr-crossorigin-anonymous">Anonymous</dfn>
+     <td><span data-x="concept-request">Requests</span> for the element will have their
      <span data-x="concept-request-mode">mode</span> set to "<code data-x="">cors</code>" and their
      <span data-x="concept-request-credentials-mode">credentials mode</span> set to "<code
      data-x="">same-origin</code>".
-    <tr>
-     <td>(the empty string)
     <tr>
      <td><dfn attr-value for="audio/crossorigin,video/crossorigin,img/crossorigin,link/crossorigin,script/crossorigin"><code data-x="attr-crossorigin-use-credentials-keyword">use-credentials</code></dfn>
      <td><dfn data-x="attr-crossorigin-use-credentials">Use Credentials</dfn>
@@ -7643,8 +7647,8 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
 
   <p>The attribute's <i data-x="missing value default">missing value default</i> is the <dfn
   data-x="attr-crossorigin-none">No CORS</dfn> state, and its <i data-x="invalid value
-  default">invalid value default</i> is the <span
-  data-x="attr-crossorigin-anonymous">Anonymous</span> state.</p>
+  default">invalid value default</i> and <i data-x="empty value default">empty value default</i> are
+  both the <span data-x="attr-crossorigin-anonymous">Anonymous</span> state.</p>
 
   <p>The majority of fetches governed by <span data-x="CORS settings attribute">CORS settings
   attributes</span> will be done via the <span>create a potential-CORS request</span> algorithm.</p>
@@ -13890,10 +13894,8 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
     <tr>
      <td><dfn attr-value for="html-global/translate"><code
      data-x="attr-translate-yes-keyword">yes</code></dfn>
-     <td rowspan=2><dfn data-x="attr-translate-yes-state">Yes</dfn>
-     <td rowspan=2>Sets <span>translation mode</span> to <span>translate-enabled</span>.
-    <tr>
-     <td>(the empty string)
+     <td><dfn data-x="attr-translate-yes-state">Yes</dfn>
+     <td>Sets <span>translation mode</span> to <span>translate-enabled</span>.
     <tr>
      <td><dfn attr-value for="html-global/translate"><code
      data-x="attr-translate-no-keyword">no</code></dfn>
@@ -13903,7 +13905,9 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
 
   <p>The attribute's <i data-x="missing value default">missing value default</i> and <i
   data-x="invalid value default">invalid value default</i> are both the <dfn
-  data-x="attr-translate-inherit-state">Inherit</dfn> state.</p>
+  data-x="attr-translate-inherit-state">Inherit</dfn> state, and its <i data-x="empty value
+  default">empty value default</i> is the <span data-x="attr-translate-yes-state">Yes</span>
+  state.</p>
 
   <p>Each element (even non-HTML elements) has a <dfn>translation mode</dfn>, which is in either the
   <span>translate-enabled</span> state or the <span>no-translate</span> state. If an <span
@@ -37731,10 +37735,8 @@ interface <dfn interface>MediaError</dfn> {
     <tr>
      <td><dfn attr-value for="audio/preload,video/preload"><code
      data-x="attr-media-preload-auto">auto</code></dfn>
-     <td rowspan=2><dfn data-x="attr-media-preload-auto-state">Automatic</dfn>
-     <td rowspan=2>Hints to the user agent that the user agent can put the user's needs first without risk to the server, up to and including optimistically downloading the entire resource.
-    <tr>
-     <td>(the empty string)
+     <td><dfn data-x="attr-media-preload-auto-state">Automatic</dfn>
+     <td>Hints to the user agent that the user agent can put the user's needs first without risk to the server, up to and including optimistically downloading the entire resource.
     <tr>
      <td><dfn attr-value for="audio/preload,video/preload"><code
      data-x="attr-media-preload-none">none</code></dfn>
@@ -37749,6 +37751,9 @@ interface <dfn interface>MediaError</dfn> {
          When the media resource is playing, hints to the user agent that bandwidth is to be considered scarce, e.g. suggesting throttling the download so that the media data is obtained at the slowest possible rate that still maintains consistent playback.
   </table>
 
+  <p>The attribute's <i data-x="empty value default">empty value default</i> is the <span
+  data-x="attr-media-preload-auto-state">Automatic</span> state.</p>
+
   <p>The attribute's <i data-x="missing value default">missing value default</i> and <i
   data-x="invalid value default">invalid value default</i> are both
   <span>implementation-defined</span>, though the <span
@@ -80348,10 +80353,8 @@ END:VCARD</pre>
    <tbody>
     <tr>
      <td><dfn attr-value for="html-global/hidden"><code data-x="attr-hidden-hidden">hidden</code></dfn>
-     <td rowspan=2><dfn data-x="attr-hidden-hidden-state">Hidden</dfn>
-     <td rowspan=2>Will not be rendered.
-    <tr>
-     <td>(the empty string)
+     <td><dfn data-x="attr-hidden-hidden-state">Hidden</dfn>
+     <td>Will not be rendered.
     <tr>
      <td><dfn attr-value for="html-global/hidden"><code data-x="attr-hidden-until-found">until-found</code></dfn>
      <td><dfn data-x="attr-hidden-until-found-state">Hidden Until Found</dfn>
@@ -80361,8 +80364,8 @@ END:VCARD</pre>
 
   <p>The attribute's <i data-x="missing value default">missing value default</i> is the <dfn
   data-x="attr-hidden-not-hidden-state">Not Hidden</dfn> state, and its <i data-x="invalid value
-  default">invalid value default</i> is the <span data-x="attr-hidden-hidden-state">Hidden</span>
-  state.</p>
+  default">invalid value default</i> and <i data-x="empty value default">empty value default</i> are
+  both the <span data-x="attr-hidden-hidden-state">Hidden</span> state.</p>
 
   <p>When an element has the <code data-x="attr-hidden">hidden</code> attribute in the <span
   data-x="attr-hidden-hidden-state">Hidden</span> state, it indicates that the element is not yet, or
@@ -83359,10 +83362,8 @@ addShortcutKeyLabel(document.getElementById('c'));</code></pre>
     <tr>
      <td><dfn attr-value for="html-global/contenteditable"><code
      data-x="attr-contenteditable-true">true</code></dfn>
-     <td rowspan=2><dfn data-x="attr-contenteditable-true-state">True</dfn>
-     <td rowspan=2>The element is editable.
-    <tr>
-     <td>(the empty string)
+     <td><dfn data-x="attr-contenteditable-true-state">True</dfn>
+     <td>The element is editable.
     <tr>
      <td><dfn attr-value for="html-global/contenteditable"><code
      data-x="attr-contenteditable-false">false</code></dfn>
@@ -83379,7 +83380,9 @@ addShortcutKeyLabel(document.getElementById('c'));</code></pre>
   <p>The attribute's <i data-x="missing value default">missing value default</i> and <i
   data-x="invalid value default">invalid value default</i> are both the <dfn
   data-x="attr-contenteditable-inherit-state">Inherit</dfn> state. The inherit state indicates that
-  the element is editable (or not) based on the parent element's state.</p>
+  the element is editable (or not) based on the parent element's state. The attribute's <i
+  data-x="empty value default">empty value default</i> is the <span
+  data-x="attr-contenteditable-true-state">True</span> state.</p>
 
   <div class="example">
    <p>For example, consider a page that has a <code>form</code> and a <code>textarea</code> to
@@ -83647,10 +83650,8 @@ body { display:none }
     <tr>
      <td><dfn attr-value for="html-global/spellcheck"><code
      data-x="attr-spellcheck-true">true</code></dfn>
-     <td rowspan=2><dfn data-x="attr-spellcheck-true-state">True</dfn>
-     <td rowspan=2>Spelling and grammar will be checked.
-    <tr>
-     <td>(the empty string)
+     <td><dfn data-x="attr-spellcheck-true-state">True</dfn>
+     <td>Spelling and grammar will be checked.
     <tr>
      <td><dfn attr-value for="html-global/spellcheck"><code
      data-x="attr-spellcheck-false">false</code></dfn>
@@ -83662,7 +83663,9 @@ body { display:none }
   data-x="invalid value default">invalid value default</i> are both the <dfn
   data-x="attr-spellcheck-default-state">Default</dfn> state. The default state indicates that the
   element is to act according to a default behavior, possibly based on the parent element's own
-  <code data-x="attr-spellcheck">spellcheck</code> state, as defined below.</p>
+  <code data-x="attr-spellcheck">spellcheck</code> state, as defined below. The attribute's <i
+  data-x="empty value default">empty value default</i> is the <span
+  data-x="attr-spellcheck-true-state">True</span> state.</p>
 
   <div w-nodev>
 
@@ -83839,11 +83842,9 @@ body { display:none }
     <tr>
      <td><dfn attr-value for="html-global/writingsuggestions"><code
      data-x="attr-writingsuggestions-true">true</code></dfn>
-     <td rowspan="2"><dfn data-x="attr-writingsuggestions-true-state">True</dfn>
-     <td rowspan="2">Writing suggestions should be offered on this element.
+     <td><dfn data-x="attr-writingsuggestions-true-state">True</dfn>
+     <td>Writing suggestions should be offered on this element.
     </tr>
-    <tr>
-     <td>(the empty string)
     <tr>
      <td><dfn attr-value for="html-global/writingsuggestions"><code
       data-x="attr-writingsuggestions-false">false</code></dfn>
@@ -83858,7 +83859,8 @@ body { display:none }
   element's own <code data-x="attr-writingsuggestions">writingsuggestions</code> state, as defined
   below.</p>
 
-  <p>The attribute's <i data-x="invalid value default">invalid value default</i> is the <span
+  <p>The attribute's <i data-x="invalid value default">invalid value default</i> and <i
+  data-x="empty value default">empty value default</i> are both the <span
   data-x="attr-writingsuggestions-true-state">True</span> state.</p>
 
   <dl class="domintro">
@@ -84190,21 +84192,19 @@ body { display:none }
     <tr>
      <td><dfn attr-value for="html-global/autocorrect"><code
      data-x="attr-autocorrect-on">on</code></dfn>
-     <td rowspan="2"><dfn data-x="concept-autocorrection-on">on</dfn>
-     <td rowspan="2">The user agent is permitted to automatically correct spelling errors while the user types.
+     <td><dfn data-x="concept-autocorrection-on">on</dfn>
+     <td>The user agent is permitted to automatically correct spelling errors while the user types.
      Whether spelling is automatically corrected while typing left is for the user agent to decide,
      and may depend on the element as well as the user's preferences.
-    <tr>
-     <td>(the empty string)
     <tr>
      <td><dfn attr-value for="html-global/autocorrect"><code data-x="attr-autocorrect-off">off</code></dfn>
      <td><dfn data-x="concept-autocorrection-off">off</dfn>
      <td>The user agent is not allowed to automatically correct spelling while the user types.
   </table>
 
-  <p>The attribute's <i data-x="invalid value default">invalid value default</i> and <i
-  data-x="missing value default">missing value default</i> are both the <span
-  data-x="concept-autocorrection-on">on</span> state.</p>
+  <p>The attribute's <i data-x="invalid value default">invalid value default</i>, <i data-x="missing
+  value default">missing value default</i>, and <i data-x="empty value default">empty value
+  default</i> are all the <span data-x="concept-autocorrection-on">on</span> state.</p>
 
   <p>The <dfn attribute for="HTMLElement"><code data-x="dom-autocorrect">autocorrect</code></dfn>
   getter steps are: return true if the element's <span>used autocorrection state</span> is <span
@@ -87367,11 +87367,9 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
     <tr>
      <td><dfn attr-value for="html-global/popover"><code
      data-x="attr-popover-auto">auto</code></dfn>
-     <td rowspan=2><dfn data-x="attr-popover-auto-state">Auto</dfn>
-     <td rowspan=2>Closes other popovers when opened; has <span data-x="popover light dismiss">light
+     <td><dfn data-x="attr-popover-auto-state">Auto</dfn>
+     <td>Closes other popovers when opened; has <span data-x="popover light dismiss">light
      dismiss</span> and responds to <span data-x="close request">close requests</span>.
-    <tr>
-     <td>(the empty string)
     <tr>
      <td><dfn attr-value for="html-global/popover"><code
      data-x="attr-popover-manual">manual</code></dfn>
@@ -87391,9 +87389,10 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
   </table>
 
   <p>The attribute's <i data-x="missing value default">missing value default</i> is the <dfn
-  data-x="attr-popover-none-state">No Popover</dfn> state, and its <i data-x="invalid value
+  data-x="attr-popover-none-state">No Popover</dfn> state, its <i data-x="invalid value
   default">invalid value default</i> is the <span data-x="attr-popover-manual-state">Manual</span>
-  state.</p>
+  state, and its <i data-x="empty value default">empty value default</i> is the <span
+  data-x="attr-popover-auto-state">Auto</span> state.</p>
 
   <p>The <dfn attribute for="HTMLElement"><code data-x="dom-popover">popover</code></dfn> IDL
   attribute must <span>reflect</span> the <span data-x="attr-popover">popover</span> attribute,