Added the composed flag as specified in the WHATWG spec (https://dom.spec.whatwg.org/#dictdef-eventinit). This flag is present in Chrome v55 and may have been respected in earlier versions as well.
Why does MDN look different?
MDN is changing to focus just on documenting web technologies. All the same great content is still here; we’re just changing some visual elements and navigation, to help you more quickly find the web technology docs you’re looking for.
But don’t worry, MDN and Mozilla are still together! In fact, we're updating MDN’s look to reflect Mozilla's new logo and colors.