Fix #511: validate external type

Signed-off-by: Zoltan Kis <[email protected]>

Author: zolkis

index.html

@@ -2742,43 +2742,73 @@ <h3><dfn>Writing or pushing content</dfn></h3>
       </p>
       <ol class=algorithm id="validate-external-type">
         <li>
-          If |input:string| is not a {{USVString}} or it is empty, or its
+          If |input:string| is not an [=ASCII string=] or it is empty, or its
           length exceeds 255 bytes, return `false`.
         </li>
         <li>
-          Let |domain| be the |input| from the start of |input| up to but
-          excluding the last occurrence of U+003A (`:`), or `null` if that is
-          not found.
-        </li>
-        <li>
-          Let |type| be the |input| after the last occurrence, if any, of
-          `U+003A` (`:`) up to the end of |input|, or `null` if that is
-          not found.
-        </li>
-        <li>
-          If |domain| or |type| is `null`, return `false`.
+          If input starts with `U+005B` (`[`), then:
+          <ol>
+            <li>
+              Let |address| be the part of input between `U+005B` (`[`) and
+              the first occurrence of `U+005D` (`]`) or `null` if that is not
+              found.
+            </li>
+            <li>
+              If |address| is `null`, return `false`.
+            </li>
+            <li>
+              Let |domain| be the result of running
+              <a href="https://url.spec.whatwg.org/#concept-ipv6-parser">
+              IPv6 parsing</a> on |address|.
+            </li>
+            <li>
+              If |domain| is failure, return `false`.
+            </li>
+            <li>
+              Let |rest| be the |input| after the first occurrence, if any, of
+              `U+005D` (`]`) up to the end of |input|, or `null` if that is
+              not found.
+            </li>
+            <li>
+              If |rest| is `null`, or it contains less than 2 [=code points=],
+              or the first [=code point=] in |rest| is not `U+003A` (`:`),
+              return `false`.
+            </li>
+            <li>
+              Let |type| be |rest| from the second [=code point=] up to the end
+              of |rest|.
+            </li>
+          </ol>
         </li>
         <li>
-          Run the following sub-steps of
-          <a href="https://url.spec.whatwg.org/#host-parsing">host parsing</a>
-          on |domain|:
-          <ul>
+          Otherwise,
+          <ol>
+            <li>
+               Let |domain| be the |input| from the start of |input| up to
+               but excluding the first occurrence of `U+003A` (`:`), or `null`
+               if that is not found.
+            </li>
+            <li>
+              Let |type| be the |input| after the first occurrence, if any, of
+              `U+003A` (`:`) up to the end of |input|, or `null` if that is
+              not found.
+            </li>
+            <li>
+              If |domain| or |type| is `null`, return `false`.
+            </li>
             <li>
               Let |asciiDomain| be the result of running
               <a href="https://url.spec.whatwg.org/#concept-domain-to-ascii">
-              domain to ASCII</a> on |domain|.
+              domain to ASCII</a> given |domain| and `true` (as |beStrict|).
             </li>
             <li>
               If |asciiDomain| is failure, return `false`.
             </li>
             <li>
-              If |asciiDomain| contains a [=forbidden host code point=],
-              return `false`.
+              If |asciiDomain| contains a [=forbidden host code point=] or
+              `U+005F` `LOW LINE` (`_`), return `false`.
             </li>
-          </ul>
-        </li>
-        <li>
-          If |type| is empty, return `false`.
+          </ol>
         </li>
         <li>
           If |type| contains [=code points=] that are not