ANSI Common Lisp   19 Filenames   19.2 Pathnames   19.2.1 Pathname Components

19.2.1.6 The Pathname Version Component

The version is either a positive integer or a symbol from the following list: nil, :wild, :unspecific, or :newest (refers to the largest version number that already exists in the file system when reading a file, or to a version number greater than any already existing in the file system when writing a new file). Implementations can define other special version symbols.