Clarify note more

Author: domfarolino

cssom-1/Overview.bs

@@ -790,7 +790,8 @@ represents a style sheet as defined by the CSS specification. In the CSSOM a
   change the corresponding attribute on the <a for=CSSStyleSheet>owner node</a>.
 
   Note: The <a for=CSSStyleSheet>owner node</a> of a <a>CSS style sheet</a>, if non-null, is the node whose <a>associated
-  CSS style sheet</a> is the <a>CSS style sheet</a> in question.
+  CSS style sheet</a> is the <a>CSS style sheet</a> in question, when the <a>CSS style sheet</a> is <a
+  lt="add a CSS style sheet">added</a>.
 
 
  <dt><dfn id=concept-css-style-sheet-title>title</dfn>