Assorted machinery having to do with just the bird code
system is relegated to a separate module, abbr.py.
The module contains an assortment of manifest constants and functions, and one class.
ABBR_L
Maximum length of a bird code, 6 in the CBC system.
BLANK_ABBR
A string containing ABBR_L spaces.
RE_ABBR
A regular expression (using Python's standard
re regular expression
module) that describes a valid bird code.
REL_SIMPLE
The relationship code for simple (non-compound) forms, one space.
REL_HYBRID
The single-character relationship code denoting
hybrids, "^".
REL_PAIR
The single-character relationship code denoting a
species pair, "|".