[selectors] Add issue about relaxing #id syntax requirements.

Author: tabatkins

selectors/Overview.html

@@ -2281,6 +2281,11 @@ <h3 id=id-selectors><span class=secno>6.7. </span> ID selectors</h3>
    An ID selector represents an element instance that has an identifier that
    matches the identifier in the ID selector.
 
+  <p class=issue> In Quirks Mode, we accept all hash tokens, not just ones
+   whose value matches the ident syntax. Should we change the Standards Mode
+   to do that, too? Note that HTML5 loosened the definition of valid ids to
+   allow things starting with numbers, etc.
+
   <p>Selectors does not specify how a UA knows the ID-typed attribute of an
    element. The UA may, e.g., read a document's DTD, have the information
    hard-coded or ask the user.

selectors/Overview.src.html

@@ -1487,6 +1487,11 @@ <h3 id="id-selectors">
   An ID selector represents an element instance that has an
   identifier that matches the identifier in the ID selector.
 
+  <p class='issue'>
+    In Quirks Mode, we accept all hash tokens, not just ones whose value matches the ident syntax.
+    Should we change the Standards Mode to do that, too?
+    Note that HTML5 loosened the definition of valid ids to allow things starting with numbers, etc.
+
   <p>Selectors does not specify how a UA knows the ID-typed attribute of
   an element. The UA may, e.g., read a document's DTD, have the
   information hard-coded or ask the user.