From the Web IDL spec: https://heycam.github.io/webidl/#idl-undefined
[...]
undefined constant values in IDL are represented with the `undefined`
token.
[...]
Note: This value was previously spelled `void`, and more limited in how
it was allowed to be used.
This is mostly to get the grunt work of the way. This is split up into
multiple commits to hopefully make it more manageable to review.
Note that these are not full implementations, and the bindings mostly
get the low hanging fruit.
Also implements some attributes that I kept out because they had
dashes in them. Therefore, this closes#2905.
Note that these aren't full implementations of the bindings. This
mostly implements the low hanging fruit (namely, basic reflections)
There are some attributes that should be USVString instead of
DOMString. However, USVString is a slightly different definition
of DOMString, so it should suffice for now.
