Input mask

In computer programming, an input mask refers to a string expression, defined by a developer, that governs what a user is allowed to enter in as input in a text box. It can be said to be a template, or set format that entered data must conform to, mainly used for the purposes of data integrity by preventing transcription errors. The syntax of this string expression differs from implementation to implementation, but the fundamental input types are all supported.

Some frequent uses of input masks include entry of telephone numbers, ZIP or postal codes, times and dates.

Generally speaking, an input mask is a user generated set of rules, so if say: only allows 45 characters, then the entry must stay up to or within 45 character, they cannot exceed this rules. This kind of string is useful in finding reports and healthcare files.

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Wikipedia