[css-cascade] Add the Cascade 4 dfn tags for origin/style sheet, and do some light rewrapping.

Author: tabatkins

css-cascade-3/Overview.bs

@@ -659,22 +659,26 @@ Cascading Origins</h3>
 	CSS defines three core <a>origins</a>:
 
 	<dl>
-		<dt id='cascade-origin-author'>Author
+		<dt><dfn export id='cascade-origin-author' lt="author origin|author style sheet">Author Origin</dfn>
 		<dd>
-			The author specifies style sheets for a source document according to the conventions of the document language. For instance, in HTML, style sheets may be included in the document or linked externally.
+			The author specifies style sheets for a source document
+			according to the conventions of the document language.
+			For instance, in HTML,
+			style sheets may be included in the document or linked externally.
 
-		<dt id='cascade-origin-user'>User
+		<dt><dfn export id='cascade-origin-user' lt="user origin|user style sheet">User Origin</dfn>
 		<dd>
 			The user may be able to specify style information for a particular document.
 			For example, the user may specify a file that contains a style sheet
 			or the user agent may provide an interface that generates a user style sheet
 			(or behaves as if it did).
 
-		<dt id='cascade-origin-ua'>User agent
+		<dt><dfn export id='cascade-origin-ua' lt="user agent origin|ua origin|user agent style sheet|ua style sheet">User Agent Origin</dfn>
 		<dd>
 			Conforming user agents must apply a default style sheet
 			(or behave as if they did).
-			A user agent's default style sheet should present the elements of the document language in ways that satisfy general presentation expectations for the document language
+			A user agent's default style sheet should present the elements of the document language
+			in ways that satisfy general presentation expectations for the document language
 			(e.g., for visual browsers, the EM element in HTML is presented using an italic font).
 			See e.g. the <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/rendering.html#the-css-user-agent-style-sheet-and-presentational-hints">HTML user agent style sheet</a>. [[HTML5]]
 	</dl>