[selectors-4] Add issue against API hooks given previous rewrite. w3c#2240

Author: fantasai

selectors-4/Overview.bs

@@ -3591,6 +3591,11 @@ API Hooks</h2>
 	To aid in the writing of specs that use Selectors concepts,
 	this section defines several API hooks that can be invoked by other specifications.
 
+	Issue: Are these still necessary now that we have more rigorous definitions for <a>match</a> and <a>invalid selector</a>?
+	Nouns are a lot easier to coordinate across specification than predicates,
+	and details like the exact order of elements returned from <code>querySelector</code>
+	seem to make more sense being defined in the DOM specification than in Selectors.
+
 <h3 id='parse-selector' algorithm>
 Parse A Selector</h3>