Make hidden input _charset_ checks case insensitive

Fixes #5914.

Author: josepharhar

source

@@ -45117,9 +45117,10 @@ interface <dfn>HTMLInputElement</dfn> : <span>HTMLElement</span> {
 
   </div>
 
-  <p>If the <code data-x="attr-fe-name">name</code> attribute is present and has a value that is
-  <span>identical to</span> "<code data-x="attr-fe-name-charset">_charset_</code>", then the
-  element's <code data-x="attr-input-value">value</code> attribute must be omitted.</p>
+  <p>If the <code data-x="attr-fe-name">name</code> attribute is present and has a value that is an
+  <span>ASCII case-insensitive</span> match for "<code
+  data-x="attr-fe-name-charset">_charset_</code>", then the element's <code
+  data-x="attr-input-value">value</code> attribute must be omitted.</p>
 
   <div class="bookkeeping">
 
@@ -52655,9 +52656,9 @@ interface <dfn>HTMLLegendElement</dfn> : <span>HTMLElement</span> {
   is no longer allowed.</p>
 
   <p>Other than <code data-x="">isindex</code>, any non-empty value for <code
-  data-x="attr-form-name">name</code> is allowed. The name <dfn><code
-  data-x="attr-fe-name-charset">_charset_</code></dfn> is special: if used as the name of a <span
-  data-x="attr-input-type-hidden">Hidden</span> control with no <code
+  data-x="attr-form-name">name</code> is allowed. An <span>ASCII case-insensitive</span> match for
+  the name <dfn><code data-x="attr-fe-name-charset">_charset_</code></dfn> is special: if used as
+  the name of a <span data-x="attr-input-type-hidden">Hidden</span> control with no <code
   data-x="attr-input-value">value</code> attribute, then during submission the <code
   data-x="attr-input-value">value</code> attribute is automatically given a value consisting of the
   submission character encoding.</p>
@@ -56368,8 +56369,8 @@ fur
      <li>
       <p>Otherwise, if the <var>field</var> element is an <code>input</code> element whose <code
       data-x="attr-input-type">type</code> attribute is in the <span
-      data-x="attr-input-type-hidden">Hidden</span> state and <var>name</var> is "<code
-      data-x="attr-fe-name-charset">_charset_</code>":</p>
+      data-x="attr-input-type-hidden">Hidden</span> state and <var>name</var> is an <span>ASCII
+      case-insensitive</span> match for "<code data-x="attr-fe-name-charset">_charset_</code>":</p>
 
       <ol>
        <li><p>Let <var>charset</var> be the <span data-x="encoding name">name</span> of