[css-transitions-2] Define order for sorting transitioncancel events

See #11064.

Author: birtles

css-transitions-2/Overview.bs

@@ -363,6 +363,11 @@ are sorted in composite order (first to last) as follows:
     such that ‘-moz-column-width’ sorts before
     ‘column-width’).
 
+When determining the composite order in order to sort transition events
+where either or both of the events is a {{transitioncancel}} event,
+use the [=owning element=] and [=transition generation=]
+that were set immediately prior to cancelling the transition.
+
 Transitions generated using the markup defined in this specification are
 <em>not</em> added to the <a>global animation list</a> when they are created.
 Instead, these animations are appended to the <a>global animation list</a> at
@@ -372,7 +377,7 @@ Transitions that have been disassociated from their <a>owning element</a>
 but are still [=play state/idle=] do not have a defined
 composite order.
 
-Note, this behavior relies on the fact that disassociating a transition
+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
 [=play state/idle|idle play state=].