[selectors-4] Cross-link to grammar from terminology sections.

Author: fantasai

selectors-4/Overview.bs

@@ -550,6 +550,8 @@ Structure and Terminology</h3>
 	<a>ID selector</a>,
 	or <a>pseudo-class</a>
 	is a <a>simple selector</a>.
+	It is represented by <<simple-selector>>
+	in the selectors <a href="#grammar">grammar</a>.
 
 	A <dfn id="compound" export>compound selector</dfn>
 	is a sequence of <a>simple selectors</a>
@@ -558,6 +560,8 @@ Structure and Terminology</h3>
 	If it contains a <a>type selector</a> or <a>universal selector</a>,
 	that selector must come first in the sequence.
 	Only one type selector or universal selector is allowed in the sequence.
+	A <a>compound selector</a> is represented by <<compound-selector>>
+	in the selectors <a href="#grammar">grammar</a>.
 
 	Note: As whitespace represents the <a>descendant combinator</a>,
 	no whitespace is allowed between the <a>simple selectors</a>
@@ -567,6 +571,8 @@ Structure and Terminology</h3>
 	a sequence of one or more <a>compound selectors</a>
 	separated by <a>combinators</a>.
 	It represents an element in a particular relationship to other elements.
+	Complex selectors are represented by <<complex-selector>>
+	in the selectors <a href="#grammar">grammar</a>.
 
 	A <dfn export for=selector>combinator</dfn> represents a particular kind of relationship
 	between the elements matched by the <a>compound selectors</a> on either side.
@@ -585,7 +591,8 @@ Structure and Terminology</h3>
 	when the type is either unimportant or specified in the surrounding prose;
 	if the type is important and unspecified,
 	it defaults to meaning a <a>list of complex selectors</a>.
-	See [[#grouping]] for further details on <a>selector lists</a>.
+	See [[#grouping]] for further details on <a>selector lists</a>
+	and the various <<*-selector-list>> productions in the <a href="#grammar">grammar</a>.
 
 	The <dfn export for=selector lt="subject|subject of a selector">subject of a selector</dfn> is
 	the element(s) that selector is defined to be about:
@@ -698,6 +705,8 @@ Relative Selectors</h3>
 	Relative selectors, once absolutized,
 	can additionally be <a>scoped</a>.
 
+	Relative selectors are represented by <<relative-selector>> in the selectors <a href="#grammar">grammar</a>.
+
 <h4 id='absolutizing'>
 Absolutizing a Relative Selector</h4>