I have already asked there. The creator of the wings plugin told me that there is no documentation about the file format and that he analysed saved xml files to get the informations he needed. I will have to do it for myself as it seems.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.