Input format validation - optional property for inputs

[viktorbenei]

Specify a regex for the input.

E.g. if only email can be specified in the input.

CON: it might be hard to solve with a reged. E.g. if you accept a list of emails, comma separated, the user might still include spaces in the list, or just messes up and includes a comma in an email. It's hard to validate a list of items, where you can write a regex for a single item easily, but a regex for the whole list can be tricky (e.g. the "comma separated email list" example).