Summary: This is legacy initializer of KeyboardEvent, but this is
implemented only by Gecko and was dropped even from DOM Level 2 spec.
There is another initiailizer, `initKeyboardEvent`, and in these days,
web developers can use KeyboardEvent constructor for initializing all
attributes with simpler syntax. So, nobody must require this unless
somebody uses web apps which can run only on Gecko.
Platform coverage: all
DevTools bug: N/A
Other browsers: Nobody has implemented this except us.
web-platform-tests: included into the second patch which tests its type.
Security and Privacy: It is one of the ways to detect Firefox, but other
Gecko specific API can use for same purpose. So, nothing must be changed
in the wild.
Masayuki Nakano <masa...@d-toybox.com
Working on DOM, Events, editor and IME handling for Gecko