maybe focus only on masking?

[tomByrer]

Seems you are expanding the scope of masking ((not showing characters as being typed) into validation (ensuring typed characters are correct for field)? I can see some cross-over, but will exponentially increase the time to get through the validation & implementation stages.

Might be useful to explore how the 2 would interact to build the masking proposal, but I can see masking-alone get through the process in a year, while validation would take many years & TBH create a bunch of code that is rarely used for all the edge cases. (eg the piping proposal has totally stalled out; too many moving parts

But if you want to dig into validation more, might be better just to label the proposal as js-input-validation-masking. I used to help out with some RegEx presets; @tunnckoCore is the main organizer there. https://github.com/regexhq