Text Field Mask versus Field Length

Hi,

Is there a way to configure a text field mask without counting the 'extra characters'?

For example, I´m trying to format a text field using 'CNPJ format' (Brazillian EIN equivalent), that has of 14 (99.999.999/9999-99), but if I let the field length 14, it will be 99.999.999/999 .

To solve this situation, the field length must be 18, but it can (and will) confuse the users.

Any sugestion?