UserForm Textbox Specific Format

Please can somebody help me.

I have created a UserForm in Excel which is complete apart from one small problem.

I have a text box into which I want the user to enter only 16 characters and I have set the max length property for this. But I also would like the data to be entered as follows, 3 Alpnumeric characters, 12 numeric characters, a “-“ and then 4 numeric characters e.g. AB-20101216-0001

If the data input does not match this criteria then a message box should appear.

Thank you.