version-regexp-alist

version-regexp-alist is a variable defined in `subr.el'.
Its value is

(("^[-_+ ]?snapshot$" . -4)
 ("^[-_+]$" . -4)
 ("^[-_+ ]?\\(cvs\\|git\\|bzr\\|svn\\|hg\\|darcs\\)$" . -4)
 ("^[-_+ ]?alpha$" . -3)
 ("^[-_+ ]?beta$" . -2)
 ("^[-_+ ]?\\(pre\\|rc\\)$" . -1))

• This variable may be risky if used as a file-local variable.

Documentation:
Specify association between non-numeric version and its priority.

This association is used to handle version string like "1.0pre2",
"0.9alpha1", etc. It's used by `version-to-list' (which see) to convert the
non-numeric part of a version string to an integer. For example:

String Version Integer List Version
"0.9snapshot" (0 9 -4)
"1.0-git" (1 0 -4)
"1.0pre2" (1 0 -1 2)
"1.0PRE2" (1 0 -1 2)
"22.8beta3" (22 8 -2 3)
"22.8 Beta3" (22 8 -2 3)
"0.9alpha1" (0 9 -3 1)
"0.9AlphA1" (0 9 -3 1)
"0.9 alpha" (0 9 -3)

Each element has the following form:

(REGEXP . PRIORITY)

Where:

REGEXP regexp used to match non-numeric part of a version string.
It should begin with the `^' anchor and end with a `$' to
prevent false hits. Letter-case is ignored while matching
REGEXP.

PRIORITY a negative integer specifying non-numeric priority of REGEXP.