Why not match.expand('\\0')?

[Magnus Lie Hetland]

I'm using the expand method of re MatchObjects, and was surprised to
find that the references don't work with group 0...

>>> import re
>>> p = re.compile('foo')
>>> m = p.match('foo')
>>> m.group(0)
'foo'
>>> m.expand('\\0')
'\x00'

Is this intended behavior? Why should group 0 behave differently from
the others?

-- 
Magnus Lie Hetland           "The mind is not a vessel to be filled,
http://hetland.org            but a fire to be lighted."  [Plutarch]