[johneth]

It's supported in iOS Safari and Chrome / Chrome for Android[1].

I'd say that's well supported, especially for the problem it's trying to solve (displaying the best keyboard for the input on mobile devices).

[1] https://caniuse.com/#feat=input-inputmode

[philnash]

Further to this, it is also why I suggested the pattern workaround for older browsers.

You shouldn't find yourself in too much trouble in a browser if you add an attribute to an element that it doesn't understand though, it will just ignore it.