[selectors] Slightly more detail in what simple selectors and combinators are.

Author: tabatkins

selectors/Overview.bs

@@ -540,7 +540,8 @@ Structure and Terminology</h3>
 	that selector comes first in the sequence.
 	Only one type selector or universal selector is allowed in the sequence.
 
-	A <dfn id="simple" export>simple selector</dfn> is either a
+	A <dfn id="simple" export>simple selector</dfn> represents an aspect of an element to be matched against.
+	A simple selector is either a
 	<a>type selector</a>,
 	<a>universal selector</a>,
 	<a>attribute selector</a>,
@@ -549,7 +550,7 @@ Structure and Terminology</h3>
 	or <a>pseudo-class</a>.
 
 	A <dfn export>combinator</dfn> represents a particular kind of relationship
-	between the <a>compound selectors</a> on either side.
+	between the elements matched by the <a>compound selectors</a> on either side.
 	Combinators in Selectors level 4 include:
 	whitespace,
 	“greater-than sign” (U+003E, <code>></code>),

selectors/Overview.html

@@ -768,7 +768,8 @@ <h3 class="heading settled heading" data-level=3.1 id=structure><span class=secn
 	that selector comes first in the sequence.
 	Only one type selector or universal selector is allowed in the sequence.
 
-<p>	A <dfn data-dfn-type=dfn data-export="" id=simple>simple selector<a class=self-link href=#simple></a></dfn> is either a
+<p>	A <dfn data-dfn-type=dfn data-export="" id=simple>simple selector<a class=self-link href=#simple></a></dfn> represents an aspect of an element to be matched against.
+	A simple selector is either a
 	<a data-link-type=dfn href=#type-selector title="type selector">type selector</a>,
 	<a data-link-type=dfn href=#universal-selector0 title="universal selector">universal selector</a>,
 	<a data-link-type=dfn href=#attribute-selector title="attribute selector">attribute selector</a>,
@@ -777,7 +778,7 @@ <h3 class="heading settled heading" data-level=3.1 id=structure><span class=secn
 	or <a data-link-type=dfn href=#pseudo-class title=pseudo-class>pseudo-class</a>.
 
 <p>	A <dfn data-dfn-type=dfn data-export="" id=combinator>combinator<a class=self-link href=#combinator></a></dfn> represents a particular kind of relationship
-	between the <a data-link-type=dfn href=#compound title="compound selectors">compound selectors</a> on either side.
+	between the elements matched by the <a data-link-type=dfn href=#compound title="compound selectors">compound selectors</a> on either side.
 	Combinators in Selectors level 4 include:
 	whitespace,
 	“greater-than sign” (U+003E, <code>&gt;</code>),