[no-unknown-property] data-* attributes should be allowed to have uppercase letters as well

[HJain13]

Technically HTML tags and their attributes are case insensitive [1]. But React types generally prevent usage of the uppercase/mixed case version of the tags and attributes as it conflicts with other established conventions (eg: treating tags with the first letter uppercase as a component in JSX). The typings for React also error out for uppercased attributes.

However, data-attributes are special in this regard; From what I can see data-testId is considered to be valid attribute even by react (though it's automatically lowercase by the browser) (TS enabled react sandbox). Right now the lint rule creates a false positive for this and I am not sure if that should be the case.

[ljharb]

for tags, not generally - jsx explicitly prevents it.

For attributes, there's a bunch of patterns - some are case sensitive, some case-insensitive. data-testId is a perfectly valid attribute - because it works, even if the browser normalizes it.

[HJain13]

Right, but what I meant to say was that: the lint rule throws an error for it.

The relevant code due to which it throws an error (the regex doesn't have A-Z)

data-testId is a perfectly valid attribute - because it works, even if the browser normalizes it.

Given this, I would think that it's a bug and should be fixed.

[ljharb]

hmm - https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/data-* says

The name must not contain any capital letters.

but i guess React and TS lowercase everything to meet that requirement. I'll update.