variable definition in php.lang and python.lang

There seems to be a strange definition in php.lang and python.lang:

$ grep :upper: *.lang
php.lang:variable = '[[:upper:]][[:word:]]*|_'
prolog.lang:variable = '[[:upper:]][[:word:]]*|_'
python.lang:variable = '[[:upper:]][[:word:]]*|_'

I believe this is correct for Prolog, but for Python or PHP ...?