Numbering system

Dear all,

My requirement: for number system is in the form of XXX.NNNNNN.Y

Where: XXX & NNNNNN is any required external number suported by DOT(.) in between the number.

and Y - Version of the document shall be incremented sequentialy i.e A,B,C etc....

Waiting for all your valuable responce.

Thank you

Seema Pilankar