This is the Rexx (and C) DLL for the new InfoZip Unzip 5.2.
This DLL adds a ZIP engine directly to the REXX language.
The list of functions in the dll, and the parameters for each, can be found in the dll source in unzip52.zip. Because there's no documentation in this package, I've included the documentation for it from the source zip here.
See also the note regarding the documentation for this DLL in the section for SREhttp/2