Intent to implement and ship: animationcancel event

Summary: Adds a new event that fires when an animation is terminated without finishing normally (e.g. element is made display:none, animation-name property is updated etc.). This parallels the recently added transitioncancel event and allows authors to know that they should not keep waiting for an

Intent to implement and ship: transitionrun, transitionstart, and,transitioncancel events

This is a follow-up to my previous intent to implement[1]. It was discovered that the implementation of transitionstart in IE10~11/Edge differs from the specification so the specification was subsequently updated to rename transitionstart to transitionrun and add IE/Edge's transitionstart e

Intent to implement: transitionstart event

Summary: CSS Transitions Level 1 defines the transitionend event but provides no means for detecting when a new transition is triggered (unlike CSS Animations which defines an animationstart event). As a result, after applying changes to content (e.g. adding a new class), authors don't kno