The new CSS canvas support could use an event that fires when the canvas is going to be used for the first time. This would allow delayed drawing of a canvas, since some canvases might never be used (like ones in :hover, :active rules). Without this event, developers are required to front-load the drawing work on page load or some other known time before the canvas might be used. Allowing the drawing to be delayed until first use also lowers memory since the buffer should be allocated when getCSSCanvasContext() is called. This event could also fire for canvas elements.