Use HTTP whitespace rather than ASCII whitespace

Tests: web-platform-tests/wpt#13615.

Fixes #89.

mimesniff.bs

@@ -217,7 +217,7 @@ a <a>valid MIME type string</a> that does not contain U+003B (;).
 <p>To <dfn export>parse a MIME type</dfn>, given a string <var>input</var>, run these steps:
 
 <ol>
- <li><p>Remove any leading and trailing <a>ASCII whitespace</a> from <var>input</var>.
+ <li><p>Remove any leading and trailing <a>HTTP whitespace</a> from <var>input</var>.
 
  <li><p>Let <var>position</var> be a <a for=string>position variable</a> for <var>input</var>,
  initially pointing at the start of <var>input</var>.
@@ -236,7 +236,7 @@ a <a>valid MIME type string</a> that does not contain U+003B (;).
  <li><p>Let <var>subtype</var> be the result of <a>collecting a sequence of code points</a> that are
  not U+003B (;) from <var>input</var>, given <var>position</var>.
 
- <li><p>Remove any trailing <a>ASCII whitespace</a> from <var>subtype</var>.
+ <li><p>Remove any trailing <a>HTTP whitespace</a> from <var>subtype</var>.
 
  <li><p>If <var>subtype</var> is the empty string or does not solely contain
  <a>HTTP token code points</a>, then return failure.
@@ -252,7 +252,12 @@ a <a>valid MIME type string</a> that does not contain U+003B (;).
    <li><p>Advance <var>position</var> to the next <a>code point</a> in <var>input</var>. (This skips
    past U+003B (;).)
 
-   <li><p><a>Skip ASCII whitespace</a> within <var>input</var> given <var>position</var>.
+   <li>
+    <p><a>Collect a sequence of code points</a> that are <a>HTTP whitespace</a> from
+    <var>input</var> given <var>position</var>.
+
+    <p class=note>This is roughly equivalent to <a>skip ASCII whitespace</a>, except that
+    <a>HTTP whitespace</a> is used rather than <a>ASCII whitespace</a>.
 
    <li><p>Let <var>parameterName</var> be the result of <a>collecting a sequence of code points</a>
    that are not U+003B (;) or U+003D (=) from <var>input</var>, given <var>position</var>.
@@ -333,7 +338,7 @@ a <a>valid MIME type string</a> that does not contain U+003B (;).
      <a>collecting a sequence of code points</a> that are not U+003B (;) from <var>input</var>,
      given <var>position</var>.
 
-     <li><p>Remove any trailing <a>ASCII whitespace</a> from <var>parameterValue</var>.
+     <li><p>Remove any trailing <a>HTTP whitespace</a> from <var>parameterValue</var>.
 
      <li><p>If <var>parameterValue</var> is the empty string, then <a for=iteration>continue</a>.
     </ol>