[css-text-4] canonicalize to extlang form prior to matching auto(<lang>)

This matches the proposed behavior for selectors 4
(see w3c#4212)

Author: frivoal

css-text-4/Overview.bs

@@ -27,16 +27,6 @@ spec: css-text-3; type: dfn
 	text: other space separator
 </pre>
 
-<pre class=biblio>
-{
-	"IANA-LANG-SUB": {
-		"href": "http://www.iana.org/assignments/language-subtag-registry",
-		"title": "IANA Language Subtag Registry",
-		"publisher": "IANA"
-	}
-}
-</pre>
-
 <h2 id="intro">
 Introduction</h2>
 
@@ -203,7 +193,10 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 			as represented in BCP 47 syntax [[BCP47]],
 			does <em>not</em> match the language range described by the computed value's <<lang>>
 			in an extended filtering operation
-			per [[RFC4647]] <cite>Matching of Language Tags</cite> (section 3.3.2),
+			per [[RFC4647]] <cite>Matching of Language Tags</cite> (section 3.3.2)
+			with both the [=content language=] and <<lang>>
+			<i>canonicalized</i> and converted to <i>extlang form</i>
+			as per section 4.5 of [[!RFC5646]],
 			then the [=used value=] is ''word-boundary-detection/manual'',
 			and this property has no effect on this element.
 			Otherwise,
@@ -214,16 +207,6 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 			the specific algorithm used is UA-dependent.
 
 			Note: This is the same matching logic as the one used for the '':lang()'' selector.
-
-			Issue: Should we allow, or require, Canonicalization of language tags and ranges,
-			as per [[RFC5646]] section 4.5,
-			together with [[IANA-LANG-SUB]]?
-			[[RFC4647]] section 3.2 says we should, and that seems appropriate.
-			The last paragraph of that same section 3.2 also says
-			we may want to consider mappings like zh-HK to zh-yue,
-			and that too seems appropriate,
-			but as far as I know there's no equivalent to [[IANA-LANG-SUB]]
-			for such mappings.
 	</dl>
 
 	<div class=example>