px:zip-load

I started writing a px:epub3-load step, but soon realized there was nothing epub-specific about it.

px:zip-load is a convenience wrapper around px:unzip, where you get a fileset and all the files inside the zip on the "fileset.out" and "in-memory.out" ports respectively.

To store the fileset to disk, simply use px:fileset-store.

I don't know if there's any point in providing a px:epub3-load alias...?