About the REX2 file format
Before ReCycle 2.0, there were two file formats associated with ReCycle: ReCycle Document files (with the extension .RCY on Windows systems) and ReCycle Export files, popularly called "REX"-files, because of its ".REX"-extension on Windows systems. The ReCycle Document Files could be saved and then re-edited in ReCycle, whereas the REX files could only be exported, once and for all, and then imported into other applications.
Since ReCycle 2.0, both these file formats are obsolete. The current format is REX2, which has the properties of both of its predecessors. REX2 files are the native ReCycle Document files, and can as such be loaded, saved and reloaded into ReCycle for continued editing and fine-tuning of slice positions and other parameters. Also, REX2 files can be imported for use in other programs by means of the REX API (which is described here).
Besides containing all the new information that ReCycle 2.0 needs, the REX2 files also have the property of being compressed (in the "zip" kind-of way, not the musical one). This is accomplished using a proprietary non-lossy algorithm which manages to reduce the size of the files by around 40-60%, in most cases.