[css-navigation-1] Reorganize spec structure a little in preparation for adding pseudo-classes too.

(This is part of importing the history from WICG/declarative-partial-updates.)

Author: dbaron

css-navigation-1/Overview.bs

@@ -36,7 +36,9 @@ url: https://html.spec.whatwg.org/multipage/browsing-the-web.html#has-been-revea
 	type: dfn; spec: html; text: has been revealed;
 </pre>
 
-<h2 id="at-route">Route queries: the ''@route'' rule</h2>
+<h2 id="condional-route-queries">Conditional rules for route queries</h2>
+
+<h3 id="at-route">Route queries: the ''@route'' rule</h3>
 
 The <dfn at-rule id="at-ruledef-route">@route</dfn> rule
 is a conditional group rule
@@ -218,6 +220,30 @@ the result of the following steps on <var>document</var>:
 The condition of the ''@route'' rule
 is the result of the <<route-condition>> in its prelude.
 
+<h3 id="route-when-function">The ''@when/route()'' function for ''@when''</h3>
+
+This specification defines an additional function for the ''@when'' rule:
+
+<pre class="prod">
+<dfn for="@when" function>route()</dfn> = route( <<route-condition>> )
+</pre>
+
+The ''@when/route()'' function is associated with the boolean result that
+its contained condition is associated with.
+
+<h3 id="route-if-function">The ''if()/route()'' function for ''if()''</h3>
+
+This specification defines an additional function for the ''if()'' function's
+<<if-test>> production:
+
+<pre class="prod">
+<dfn for="if()" function>route()</dfn> = route( <<route-condition>> )
+</pre>
+
+ISSUE: This should probably have a more formal definition of the function,
+but I can't find the formal definitions of the existing ''if()'' functions
+to model it after.
+
 <h2 id="urlpattern-function">The ''urlpattern()'' function</h2>
 
 <!--
@@ -270,27 +296,3 @@ using the steps of the <dfn>create a URL pattern for urlpattern()</dfn> algorith
 NOTE:  This function requires that its argument is quoted.
 This differs from the ''url()'' function,
 which allows its argument to be quoted or unquoted.
-
-<h2 id="route-when-function">The ''@when/route()'' function for ''@when''</h2>
-
-This specification defines an additional function for the ''@when'' rule:
-
-<pre class="prod">
-<dfn for="@when" function>route()</dfn> = route( <<route-condition>> )
-</pre>
-
-The ''@when/route()'' function is associated with the boolean result that
-its contained condition is associated with.
-
-<h2 id="route-if-function">The ''if()/route()'' function for ''if()''</h2>
-
-This specification defines an additional function for the ''if()'' function's
-<<if-test>> production:
-
-<pre class="prod">
-<dfn for="if()" function>route()</dfn> = route( <<route-condition>> )
-</pre>
-
-ISSUE: This should probably have a more formal definition of the function,
-but I can't find the formal definitions of the existing ''if()'' functions
-to model it after.