From what I have garnered from object information of the ZIP, a couple useful features are missing:
A couple trivial things, but they would greatly expand the practical uses of ZIP object, such as an use as save file.
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Removing files isn't actually supported by the ZLIB API (and I don't actually see why it'd be that useful, though if you have a particular example it's doable by other methods).
Password protection is fairly useful, so I'll add it to the request list for a future build.
For example I'm going to use hashtables for each entity, if a number of entities gets into hundreds, I imagine simply saving hashtables would result in hundreds of small files. Not good. So I was thinking I could dump them into the ZIP.
On another thought, I guess there is no point of removing a specific file at all if I'm just using this to save and load the game. Either load all or don't load at all. Dynamic file structure - such as some sort of database - would probably be better off with something other than the ZIP due to the performance hit.
Edit: Funny thing, I was experiencing a crash on closing the application until I removed the ZIP object. All I could get was runtime error popup, which disappeared too quickly.