Input mask
Also called: Formatted input
A field that formats what you type automatically, like adding spaces to a card number or slashes to a date.
Definition
Input masks help users enter structured data, but they often break paste, autofill, deleting and international formats. Testers check that pasting a full value works, that the mask fits every supported country, and that the saved value is clean.
In practice
A phone field forces the US format (555) 555-1234, so a UK number can't be entered and pasting "+44 7700 900123" turns into nonsense.