Adding new label's format

Hello.

I'm working for a labels manufaturer and I would like to add our format in libreoffice.
We have customers who have asked for it in the past.

How is the best way to perform this ?

I found in the past that all informations are in a xml file (don't remember where now).
There is a description of this file to give the good informations ?

Thanks in advance.

Sylvain Fauveau