Difference between "ASCII alphabetic character required. A-Z, a-z. a" and "ASCII alphabetic character permitted but not required." on QLineEdit input

[musimbate]

What is the difference between the following two settings for input mask on a QLineEdit.So far i find that they have the same effect.I suspect there is something I am not seeing.

A ASCII alphabetic character required. A-Z, a-z.
a ASCII alphabetic character permitted but not required._

Thanks.