[css-transitions-2] Make CSS transitions that are not tied to markup target the animations level of the cascade

Fixes w3c#2049.

Author: birtles

css-transitions-2/Overview.bs

@@ -171,6 +171,17 @@ Note, this behavior relies on the fact that disassociating a transition
 from its <a>owning element</a> always causes it to enter (or remain) in the
 <a>idle play state</a>.
 
+## Animation cascade level ## {#cascade-level}
+
+Animations with an [=animation class=] of &lsquo;CSS Transition&rsquo;
+that have an [=owning element=]
+are applied to the &lsquo;Transitions declaration&rsquo; level
+of the CSS cascade.
+All other animations generated by the markup defined in this specification,
+including animations that no longer have an [=owning element=],
+are applied to the &lsquo;Animation declarations&rsquo; level of the cascade.
+(See [[web-animations-1#applying-the-composited-result]].)
+
 # Transition Events # {#transition-events}
 
 ## Event dispatch ## {#event-dispatch}