#1278 Highlight HTML5 custom data attribute as known attribute

[Zufu Liu]

https://developer.mozilla.org/en-US/docs/Learn/HTML/Howto/Use_data_attributes
https://www.w3.org/TR/html5/single-page.html#custom-data-attribute

Since starts_with is C++20, strncmp is used.

[Zufu Liu]

Updated patch with comment.

[Neil Hodgson]

Isn't this handled by using a prefix keyword ^data- as is done in SciTE?

[Zufu Liu]

OK, completely fogot about prefix keyword.
This can be closed as invalid of something.

Maybe anothor prefix can be added ^aria-
https://www.w3.org/TR/html-aria/

[Neil Hodgson]

There appears to be a discrete list of valid "aria-" values like "aria-haspopup" and "aria-atomic" so a prefix doesn't appear correct as it would highlight invalid values as well.

[Zufu Liu]

OK, they can be added later when the draft become a W3C Recommendation, alongside with HTML 5.3.