Works may be distributed for playing with in a separate interpreter. In which case they are often made available in the Blorb package format that many interpreters support. A filename ending .zblorb is a story file intended for a Z-machine in a Blorb wrapper, while a filename ending .gblorb is a story file intended for a Glulx in a Blorb wrapper. It is not common but IF files are sometimes also seen without a Blorb wrapping, though this usually means cover art, help files, and so forth are missing, like a book with the covers torn off. Z-machine story files usually have names ending .z5 or .z8, the number being a version number, and Glulx story files usually end .ulx.