[css-transitions] Use event markup for transitionend.

Author: dbaron

css-transitions/Overview.bs

@@ -1412,10 +1412,10 @@ spec:css-values-3; type:type; text:<time>
       </p>
       <dl>
         <dt>
-          <b><dfn>transitionend</dfn></b>
+          <b><dfn event for="Element" id="transitionend">transitionend</dfn></b>
         </dt>
         <dd>
-          The <code><a>transitionend</a></code> event occurs at the completion of the transition. In the
+          The {{transitionend}} event occurs at the completion of the transition. In the
           case where a transition is removed before completion, such as if the
           transition-property is removed, then the event will not fire.
           <ul>

css-transitions/Overview.html

@@ -2292,12 +2292,12 @@ <h2 class="heading settled" data-level="6" id="transition-events"><span class="s
       <dl>
 
         <dt>
-          <b><dfn data-dfn-type="dfn" data-noexport="" id="transitionend">transitionend<a class="self-link" href="#transitionend"></a></dfn></b>
+          <b><dfn class="idl-code" data-dfn-for="Element" data-dfn-type="event" data-export="" id="transitionend">transitionend<a class="self-link" href="#transitionend"></a></dfn></b>
         </dt>
 
 
         <dd>
-          The <code><a data-link-type="dfn" href="#transitionend">transitionend</a></code> event occurs at the completion of the transition. In the
+          The <code class="idl"><a data-link-type="idl" href="#transitionend">transitionend</a></code> event occurs at the completion of the transition. In the
           case where a transition is removed before completion, such as if the
           transition-property is removed, then the event will not fire.