Update how the enforcement is done

Author: lukewarlow

dom.bs

@@ -6406,33 +6406,17 @@ given a <var>document</var>, <var>localName</var>, <var>namespace</var>, and opt
 <ol>
  <li><p>Let <var>oldValue</var> be <var>attribute</var>'s <a for=Attr>value</a>.</p></li>
 
- <li><p><a>Verify and set attribute value</a> <var>value</var> for <var>attribute</var>, with
- <var>attribute</var>'s <a for=Attr>element</a>.
+ <li><p>Set <var>attribute</var>'s <a for=Attr>value</a> to <var>value</var>.
 
- <li><p>If <var>attribute</var>'s <a for=Attr>element</a>
- <a lt="has an attribute">has an attribute</a>, then <a>handle attribute changes</a> for
- <var>attribute</var> with <var>attribute</var>'s <a for=Attr>element</a>, <var>oldValue</var>, and
- <var>value</var>.
-
- <li><p>Otherwise, throw an "{{InvalidStateError!!exception}}" {{DOMException}}.
+ <li><p><a>Handle attribute changes</a> for <var>attribute</var> with <var>attribute</var>'s
+ <a for=Attr>element</a>, <var>oldValue</var>, and <var>value</var>.
 </ol>
 
 <p>To <dfn export id=concept-element-attributes-append lt="append an attribute">append</dfn> an
-<a>attribute</a> <var>attribute</var> to an <a for=/>element</a> <var>element</var>, with an
-optional boolean <var>validate</var> (default true):
+<a>attribute</a> <var>attribute</var> to an <a for=/>element</a> <var>element</var>, run these
+steps:
 
 <ol>
- <li>
-  <p>If <var>validate</var> is true:
-
-  <ol>
-   <li><p><a>Verify and set attribute value</a>
-   <var>attribute</var>'s <a for="Attr">value</a> for <var>attribute</var>, with <var>element</var>.
-
-   <li><p>If <var>element</var> <a lt="has an attribute">has</a> an <a>attribute</a>
-   <var>attribute</var>, then throw an "{{InvalidStateError!!exception}}" {{DOMException}}.
-  </ol>
-
  <li><p><a for=list>Append</a> <var>attribute</var> to <var>element</var>'s
  <a for=Element>attribute list</a>.
 
@@ -6461,9 +6445,6 @@ optional boolean <var>validate</var> (default true):
 <a>attribute</a> <var>oldAttr</var> with an <a>attribute</a> <var>newAttr</var>, run these steps:
 
 <ol>
- <li><p><a>Verify and set attribute value</a> <var>newAttr</var>'s <a for="Attr">value</a> for
- <var>newAttr</var>, with <var>oldAttr</var>'s <a for=Attr>element</a>.
-
  <li><p><a for=list>Replace</a> <var>oldAttr</var> by <var>newAttr</var> in <var>oldAttr</var>'s
  <a for=Attr>element</a>'s <a for=Element>attribute list</a>.
 
@@ -6477,16 +6458,14 @@ optional boolean <var>validate</var> (default true):
  <a for=Attr>value</a>.
 </ol>
 
-<p>To <dfn>verify and set attribute value</dfn>
+<p>To <dfn>verify attribute value</dfn>
 {{TrustedType}} or string <var>value</var> for an <a>attribute</a> <var>attribute</var>, given an
 <a for=/>Element</a> <var>element</var>:
 
 <ol>
- <li><p>Let <var>verifiedValue</var> be the result of calling
+ <li><p>Return the result of calling
  <a abstract-op>get Trusted Types-compliant attribute value</a> for <var>attribute</var>, with
  <var>element</var>, <var>value</var>. [[!TRUSTED-TYPES]]
-
- <li><p>Set <var>attribute</var>'s <a for=Attr>value</a> to <var>verifiedValue</var>.
 </ol>
 
 <hr>
@@ -6551,6 +6530,11 @@ string <var>namespace</var> (default null):</p>
 
  <li><p>If <var>oldAttr</var> is <var>attr</var>, return <var>attr</var>.
 
+ <li><p>Let <var>verifiedValue</var> be the result of calling <a>verify attribute value</a>
+ <var>attr</var>'s <a for=Attr>value</a> for <var>attr</var>, with <var>element</var>.
+
+ <li><p>Set <var>attr</var>'s <a for=Attr>value</a> to <var>verifiedValue</var>.
+
  <li><p>If <var>oldAttr</var> is non-null, then <a lt="replace an attribute">replace</a>
  <var>oldAttr</var> with <var>attr</var>.
 
@@ -6571,14 +6555,30 @@ or string <var>namespace</var> (default null):
  <a lt="get an attribute by namespace and local name">getting an attribute</a> given
  <var>namespace</var>, <var>localName</var>, and <var>element</var>.
 
- <li>If <var>attribute</var> is null, create an <a>attribute</a> whose <a for=Attr>namespace</a> is
- <var>namespace</var>, <a for=Attr>namespace prefix</a> is <var>prefix</var>,
- <a for=Attr>local name</a> is <var>localName</var>, <a for=Attr>value</a> is <var>value</var>, and
- <a for=Node>node document</a> is <var>element</var>'s <a for=Node>node document</a>, then
- <a lt="append an attribute">append</a> this <a>attribute</a> to <var>element</var>, and then
- return.
+ <li><p>Let <var>attributeExists</var> be false if <var>attribute</var> is null, and true otherwise.
+
+ <li><p>If <var>attributeExists</var> is false, set <var>attribute</var> to an <a>attribute</a>
+ whose <a for=Attr>namespace</a> is <var>namespace</var>, <a for=Attr>namespace prefix</a> is
+ <var>prefix</var>, <a for=Attr>local name</a> is <var>localName</var>, <a for=Attr>value</a> is
+ <var>value</var>, and <a for=Node>node document</a> is <var>element</var>'s <a for=Node>node
+ document</a>.
 
- <li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>value</var>.
+ <li><p>Let <var>verifiedValue</var> be the result of calling <a>verify attribute value</a>
+ <var>value</var> for <var>attribute</var>, with <var>element</var>.
+
+ <li><p>Set <var>attributeExists</var> to true if <var>element</var> <a lt="has an attribute">has
+ an attribute</a> <var>attribute</var>; otherwise false.
+
+ <li><p>If <var>attributeExists</var> is true, <a lt="change an attribute">change</a>
+ <var>attribute</var> to <var>verifiedValue</var>.
+
+ <li><p>Otherwise:
+  <ol>
+   <li><p>Set <var>attribute</var>'s <a for=Attr>value</a> to <var>verifiedValue</var>.
+
+   <li><p><a lt="append an attribute">Append</a> this <a>attribute</a> to
+   <var>element</var>.
+  </ol>
 </ol>
 </div>
 
@@ -6839,12 +6839,25 @@ method steps are:
  and null otherwise.
  <!-- This is step 2 of "get an attribute by name", modified as appropriate -->
 
- <li><p>If <var>attribute</var> is null, create an <a>attribute</a> whose
- <a for=Attr>local name</a> is <var>qualifiedName</var>, <a for=Attr>value</a> is
- <var>value</var>, and <a for=Node>node document</a> is <a>this</a>'s <a for=Node>node document</a>,
- then <a lt="append an attribute">append</a> this <a>attribute</a> to <a>this</a>, and then return.
+ <li><p>Let <var>attributeExists</var> be false if <var>attribute</var> is null, and true otherwise.
+
+ <li><p>If <var>attributeExists</var> is false, set <var>attribute</var> to an <a>attribute</a>
+ whose <a for=Attr>local name</a> is <var>qualifiedName</var>, <a for=Attr>value</a> is
+ <var>value</var>, and <a for=Node>node document</a> is <a>this</a>'s <a for=Node>node
+ document</a>.
+
+ <li><p>Let <var>verifiedValue</var> be the result of calling <a>verify attribute value</a>
+ <var>value</var> for <var>attribute</var>, with <a>this</a>.
 
- <li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>value</var>.
+ <li><p>Set <var>attribute</var>'s <a for=Attr>value</a> to <var>verifiedValue</var>.
+
+ <li><p>Set <var>attributeExists</var> to true if <a>this</a> <a lt="has an attribute">has an
+ attribute</a> <var>attribute</var>; otherwise false.
+
+ <li><p>If <var>attributeExists</var> is true, <a lt="change an attribute">change</a>
+ <var>attribute</var> to <var>value</var>.
+
+ <li><p>Otherwise <a lt="append an attribute">append</a> this <a>attribute</a> to <a>this</a>.
 </ol>
 
 <p>The
@@ -7414,7 +7427,13 @@ string <var>value</var>, run these steps:
  <li><p>If <var>attribute</var>'s <a for=Attr>element</a> is null, then set <var>attribute</var>'s
  <a for=Attr>value</a> to <var>value</var>.
 
- <li><p>Otherwise, <a lt="change an attribute">change</a> <var>attribute</var> to <var>value</var>.
+ <li><p>Otherwise:
+  <ol>
+    <li><p>Let <var>verifiedValue</var> be the result of calling <a>verify attribute value</a>
+    <var>value</var> for <var>attribute</var>, with <a>this</a>.
+
+   <li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>verifiedValue</var>.
+  </ol>
 </ol>
 
 <p>The {{Attr/value}} setter steps are to <a>set an existing attribute value</a> with <a>this</a>