Dual Format Or Input Mask???

Hi,

I am creating a database where the serialID can be a number of different 'formats'. TBH, I don't know if this can even be done in the first place, but on the off chance that it can....:p

Firstly, i'm not sure whether to use Input Mask or Format...

But the serial may be '1234567AB', '12345678AB' or '12AB1234AB'.

Or to put another way

'7 numbers 2 letters',

'8 numbers 2 letters'

or '2 numbers, 2 letters, 4 numbers, 2 letters'

I have tried creating a mask such as '00LL0000LL' (can't remember exactly, had some '9's in there too some where...) but just keep hitting a brick wall, whereby it not satisfying all of the types.

Any help much appreciated, Ben