[selectors-4] Remove section on slots and flags, since it doesn't make much sense, nothing else in the spec depends on this text, and the fact that we're using information outside the document tree is very explicitly explained in the sections on pseudo-elements and pseudo-classes already.

Author: fantasai

selectors/Overview.bs

@@ -597,23 +597,6 @@ Data Model</h3>
 		and can't be matched by <em>any</em> <a>pseudo-class</a> except for '':host'' and '':host-context()''.)
 	</div>
 
-	In addition to the information present in the document tree,
-	for the purpose of selectors,
-	elements are assumed to have arbitrary <a>pseudo-class</a> flags
-	and <a>pseudo-element</a> slots,
-	as defined by the given <a>pseudo-class</a> and <a>pseudo-element</a>.
-
-	<div class='example'>
-		For example, the first element child of each element
-		has a flag indicating that it matches the '':first-child'' pseudo-class.
-
-		For another example,
-		all elements have ''::before'' pseudo-elements,
-		but not only elements with <a>shadow trees</a> have ''::shadow'' pseudo-elements.
-	</div>
-
-	Issue: This section is imho unnecessary, and asserting the existence of a "first-child" flag belonging to the element is a) silly, because that information is already in the tree and b) confusing, because one could then interpret that as meaning the element keeps its first-child flag even when it is moved in the DOM.
-
 <h3 id="scoping">
 Scoped Selectors</h3>