Question: How to decompress Extension Files?

I am working on a program that can generate custom TCG cards and I am looking for ways to automate the process of adding the cards into Vassal through generating Extension Files. I have found that Vassal Module files are just zip files, but extensions seem to have a different formatting. I’d like to know how the different Vassal files could be decompressed and if possible edited by my own code.

I was trying to trace back the code in the source code, but I am not that familiar with Java and didn’t find anything related to this… This is my first time writing on this forum so I don’t know if this is the right place to ask this, if I am to ask somewhere else I will do so.

My experience has been that I could unzip a Vassal module extension file just as I can an ordinary module file. Maybe provide an example of what you are doing, for more help ?