Define identifiers and strings <http://lists.w3.org/Archives/Public/www-style/2009Mar/0148.html> issue 2

Author: fantasai

selectors3/Overview.html

@@ -923,8 +923,9 @@ <h4><a name=attribute-representation>6.3.1. Attribute presence and value selecto
   pseudo-class</a>.</dd>
 </dl>
 
-<p>Attribute values must be identifiers or strings. The
-case-sensitivity of attribute names and values in selectors depends on
+<p>Attribute values must be CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
+or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>. <a href="#refsCSS21">[CSS21]</a>
+The case-sensitivity of attribute names and values in selectors depends on
 the document language.</p>
 
 <div class="example">
@@ -1003,8 +1004,9 @@ <h4><a name=attribute-substrings></a>6.3.2. Substring matching attribute
   the selector does not represent anything.</dd>
 </dl>
 
-<p>Attribute values must be identifiers or strings. The
-case-sensitivity of attribute names in selectors depends on the
+<p>Attribute values must be CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>
+or <a href="http://www.w3.org/TR/CSS21/syndata.html#strings">strings</a>. <a href="#refsCSS21">[CSS21]</a>
+The case-sensitivity of attribute names in selectors depends on the
 document language.</p>
 
 <div class="example">
@@ -1204,7 +1206,8 @@ <h3><a name=id-selectors>6.5. ID selectors</a></h3>
 assign an identifier to one element instance in the document tree. An
 ID selector contains a &quot;number sign&quot; (U+0023,
 <code>#</code>) immediately followed by the ID value, which must be an
-identifier. An ID selector represents an element instance that has an
+CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifiers</a>.
+An ID selector represents an element instance that has an
 identifier that matches the identifier in the ID selector.</p>
 
 <p>Selectors does not specify how a UA knows the ID-typed attribute of
@@ -1428,7 +1431,8 @@ <h4><a name=lang-pseudo>6.6.3. The language pseudo-class :lang</a></h4>
 element's language value is performed case-insensitively.
 The identifier C does not have to be a valid language name.</p>
 
-<p>C must not be empty. (If it is, the selector is invalid.)</p>
+<p>C must be a valid CSS <a href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">identifier</a> <a href="#refsCSS21">[CSS21]</a>
+and must not be empty. (Otherwise, the selector is invalid.)</p>
 
 <p class="note"><strong>Note:</strong> It is recommended that
 documents and protocols indicate language using codes from BCP 47 <a