Rewrite the intro to be a bit simpler and clearer.

Author: tabatkins

selectors4/Overview.html

@@ -463,20 +463,16 @@ <h2 id=context><span class=secno>1. </span> Introduction</h2>
 
   <p><em>This section is not normative.</em>
 
-  <p>Selectors define the following function for elements in a tree
-   structure:
+  <p> A selector is a boolean predicate that takes an element in a tree
+   structure and answers whether the element matches the selector or not.
 
-  <pre>expression ∗ element → boolean</pre>
-
-  <p>That is, given an element and a selector, this specification defines
-   whether that element matches the selector.
-
-  <p>These expressions can also be used, for instance, to select a set of
-   elements, or a single element from a set of elements, by evaluating the
-   expression across all the elements in a subtree. <abbr
-   title="Simple Tree Transformation   Sheets">STTS</abbr> (Simple Tree
-   Transformation Sheets), a language for transforming XML trees, uses this
-   mechanism. <a href="#STTS3" rel=biblioentry>[STTS3]<!--{{STTS3}}--></a>
+  <p> These expressions can be used directly on an element to test whether it
+   matches some criteria, such as in the <code>Element.matches()</code>
+   function defined in <a href="#SELECTORS-API2"
+   rel=biblioentry>[SELECTORS-API2]<!--{{SELECTORS-API2}}--></a>, or
+   alternately, can be applied to an entire tree of elements to filter it
+   into a set of elements that match the criteria, such as in the selector in
+   a CSS style rule.
 
   <p>Selectors Levels 1, 2, and 3 are defined as the subsets of selector
    functionality defined in the <a
@@ -4149,15 +4145,6 @@ <h3 id=informative-references><span class=secno>20.2. </span> Informative
     </dd>
    <!---->
 
-   <dt id=STTS3>[STTS3]
-
-   <dd>Daniel Glazman. <a href="http://www.w3.org/TR/NOTE-STTS3"><cite>Simple
-    Tree Transformation Sheets 3.</cite></a> Electricité de France. 11
-    November 1998. Submission to the W3C. URL: <a
-    href="http://www.w3.org/TR/NOTE-STTS3">http://www.w3.org/TR/NOTE-STTS3</a>
-    </dd>
-   <!---->
-
    <dt id=SVG11>[SVG11]
 
    <dd>Erik Dahlström; et al. <a

selectors4/Overview.src.html

@@ -95,19 +95,18 @@ <h2 id="context">
 
   <p><em>This section is not normative.</em>
 
-  <p>Selectors define the following function for elements in a tree structure:</p>
-
-  <pre>expression &#x2217; element &rarr; boolean</pre>
-
-  <p>That is, given an element and a selector, this specification
-  defines whether that element matches the selector.</p>
+  <p>
+    A selector is a boolean predicate
+    that takes an element in a tree structure
+    and answers whether the element matches the selector or not.
 
-  <p>These expressions can also be used, for instance, to select a set
-  of elements, or a single element from a set of elements, by
-  evaluating the expression across all the elements in a
-  subtree. <abbr title="Simple Tree Transformation
-  Sheets">STTS</abbr> (Simple Tree Transformation Sheets), a
-  language for transforming XML trees, uses this mechanism. [[STTS3]]</p>
+  <p>
+    These expressions can be used directly on an element to test whether it matches some criteria,
+    such as in the <code>Element.matches()</code> function defined in [[SELECTORS-API2]],
+    or alternately,
+    can be applied to an entire tree of elements
+    to filter it into a set of elements that match the criteria,
+    such as in the selector in a CSS style rule.
 
   <p>Selectors Levels 1, 2, and 3 are defined as the subsets of selector
   functionality defined in the <a href="http://www.w3.org/TR/REC-CSS1">CSS1</a>,