CSS Painting API - Web APIs
paintrenderingcontext2d implements a subset of the canvasrenderingcontext2d api.
... dictionaries paintrenderingcontext2dsettings a dictionary providing a subset of canvasrenderingcontext2d settings.

Using the CSS Painting API - Web APIs
the 2d rendering context is a subset of the html5 canvas api; the version available to houdini (called the paintrenderingcontext2d) is a further subset containing most of the features available in the full canvas api with the exception of the canvasimagedata, canvasuserinterface, canvastext, and canvastextdrawingstyles apis.