I appreciate the attempt to include compatibility tables, but they're nowhere near detailed enough for serious usage. Take the canvas element as an example. The WHATWG spec has one "CanIUse" sidebar for basically each section, if that. But compatibility issues exist at the level of individual methods. E.g. .filter and .resetTransform() both have very low cross-platform support ([1] and [2]), which I can tell at a glance from MDN, both in the sidebar listing them, and the compatibility tables on each page. Whereas the WHATWG spec doesn't even mention that these are experimental ([3] and [4]), and the CanIUse sidebar is totally absent for them.
StackOverflow is not a reference, and the answers for even popular queries are sometimes a decade out of date.