[css-cascade-6] Silence "multiple possible dfn" warnings (#11162)

Author: andruud

css-cascade-6/Overview.bs

@@ -24,12 +24,15 @@ spec:dom; type:dfn;
 	text:shadow tree
 	for:tree; text:root
 	text:shadow root; for:/
+spec:dom; type:dfn; text:parent element
 spec:css-color-4; type:property; text:color
 spec:css-values-3; type: value; text:ex
 spec:css-conditional-3; type:at-rule; text:@media
 spec:mediaqueries-4; type:type; for:@media; text:all
 spec:mediaqueries-4; type:type; text:<media-query>
 spec:selectors-4; type:dfn; text:subject
+spec:selectors-4; type:dfn; text:selector
+spec:selectors-4; type:dfn; text:combinator
 spec:html; type:element; text:style
 spec:css-scoping-1; type:dfn; text:shadow host
 </pre>