Input Masks: Violating User Expectations
Because there are no standardized, widely accepted behaviors for input masks, it’s best to avoid «magical» behaviour (e.g. automatically entering characters that the user did not type), or, if you do need magical behavior, also account for user behavior that does not expect magical behavior.
For example, if the field auto-tabs to the next field, and the user also tabs right after filling in a field, it might be best to ignore the user’s tab.
[…]
If you create a new control that kind of looks like an existing control, the new control should not violate people’s expected behavior of the existing control. In other words, text fields with input masks’ behavior should be as close to a normal text field’s behavior as possible.
