[css-scoping] Define 'in the context of a shadow tree'.

Author: tabatkins

css-scoping/Overview.bs

@@ -250,6 +250,17 @@ Shadow DOM Selection Model</h3>
 	and their descendants,
 	ordered by a pre-order traversal.
 
+	A selector is <dfn>in the context of a shadow tree</dfn>
+	if it is in a stylesheet attached to the shadow tree
+	(that is, present in the <code>ShadowRoot.styleSheets</code> list),
+	or it is used in an API that is <dfn>rooted in a shadow tree</dfn>.
+
+	<div class='issue'>
+		Need to get DOM to hook this term.
+		<code>querySelector()</code>/etc are <a>rooted in a shadow tree</a>
+		if they're called on a ShadowRoot or an element in a shadow tree.
+	</div>
+
 <h4 id='host-element-in-tree'>
 Host Elements in a Shadow Tree</h4>
 
@@ -308,7 +319,7 @@ Shadow DOM Selectors</h3>
 Selecting Into the Light: the '':host'', '':host()'', and '':host-context()'' pseudo-classes</h4>
 
 	The <dfn selector>:host</dfn> pseudo-class,
-	when evaluated in the context of a <a>shadow tree</a>,
+	when evaluated <a>in the context of a shadow tree</a>,
 	matches the <a>shadow tree's</a> <a>host element</a>.
 	In any other context,
 	it matches nothing.
@@ -318,7 +329,7 @@ Selecting Into the Light: the '':host'', '':host()'', and '':host-context()'' ps
 
 	<pre>:host( <<compound-selector>> )</pre>
 
-	When evaluated in the context of a <a>shadow tree</a>,
+	When evaluated <a>in the context of a shadow tree</a>,
 	it matches the <a>shadow tree's</a> <a>host element</a>
 	if the <a>host element</a>,
 	in its normal context,
@@ -366,7 +377,7 @@ Selecting Into the Light: the '':host'', '':host()'', and '':host-context()'' ps
 
 	<pre>:host-context( <<compound-selector>> )</pre>
 
-	When evaluated in the context of a <a>shadow tree</a>,
+	When evaluated <a>in the context of a shadow tree</a>,
 	the '':host-context()'' pseudo-class matches the <a>host element</a>,
 	if the <a>host element</a> or one of its ancestors matches the provided <<compound-selector>>.
 	For the purpose of this pseudo-class,