[selectors] Try to clarify the 'stuff not under the control of selectors' part more.

Author: tabatkins

selectors/Overview.html

@@ -1550,15 +1550,17 @@ <h3 id=case-sensitive><span class=secno>3.6. </span> Characters and case
    sensitivity</h3>
 
   <p>All Selectors syntax is case-insensitive within the ASCII range (i.e.
-   [a-z] and [A-Z] are equivalent), except for the parts that are not under
-   the control of Selectors. The case-sensitivity of document language
-   element names, attribute names, and attribute values depends on the
-   document language. For example, <a
+   [a-z] and [A-Z] are equivalent), except for the following parts, which are
+   not under the control of Selectors: the case-sensitivity of document
+   language element names, attribute names, and attribute values depends on
+   the document language. For example, <a
    href="http://www.whatwg.org/html/selectors.html#case-sensitivity">in HTML,
    element names are case-insensitive</a>, but in XML, they are
    case-sensitive. Case sensitivity of namespace prefixes is defined in <a
    href="#CSS3NAMESPACE"
-   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>.
+   rel=biblioentry>[CSS3NAMESPACE]<!--{{!CSS3NAMESPACE}}--></a>. Case
+   sensitivity of <a href="#language-range"><i>language ranges</i></a> is
+   defined in the <a href="#lang-pseudo"><code>:lang()</code></a> section.
 
   <p><dfn id=whitespace>White space</dfn> in Selectors consists of the
    characters SPACE (U+0020), TAB (U+0009), LINE FEED (U+000A), CARRIAGE

selectors/Overview.src.html

@@ -823,8 +823,9 @@ <h3 id="case-sensitive">
 
   <p>All Selectors syntax is case-insensitive within the ASCII range
   (i.e. [a-z]  and [A-Z] are equivalent),
-  except for the parts that are not under the control of Selectors.
-  The case-sensitivity of
+  except for the following parts,
+  which are not under the control of Selectors:
+  the case-sensitivity of
   document language element names,
   attribute names,
   and attribute values
@@ -833,6 +834,7 @@ <h3 id="case-sensitive">
   <a href="http://www.whatwg.org/html/selectors.html#case-sensitivity">in HTML, element names are case-insensitive</a>,
   but in XML, they are case-sensitive.
   Case sensitivity of namespace prefixes is defined in [[!CSS3NAMESPACE]].
+  Case sensitivity of <i>language ranges</i> is defined in the <code>:lang()</code> section.
 
   <p><dfn id="whitespace">White space</dfn> in Selectors consists of the
   characters SPACE (U+0020), TAB (U+0009), LINE FEED (U+000A),