CLCS

Restrictions on Examining a Pathname Version Component

The version can be any symbol or any integer.

The symbol :newest refers to the largest version number that already exists in the file system when reading, overwriting, appending, superseding, or directory listing an existing file. The symbol :newest refers to the smallest version number greater than any existing version number when creating a new file.

The symbols nil, :unspecific, and :wild have special meanings and restrictions; see Special Pathname Component Values and Restrictions on Constructing Pathnames.

Other symbols and integers have implementation-defined meaning.