Remove the stray sentence that editing hosts outside a document canno…

…t have a selection

Preceeding paragraphs make it clear that selection is a concept of a document and nothing else.

index.html

@@ -109,8 +109,7 @@ <h2>
       <p>
         This one <a>selection</a> must be shared by all the content of the
         <a>document</a> (though not by nested <a>documents</a>), including any
-        [=editing hosts=] in the document. [=Editing hosts=] that are not
-        inside a <a>document</a> cannot have a <a>selection</a>.
+        [=editing hosts=] in the document.</a>.
       </p>
       <p>
         Each <a>selection</a> can be associated with a single <a>range</a>.