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
"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.