def METHOD_NAME(env, target=None, source=_null, **kw):
  """ Wrapper for _POFileBuilder. We use it to make user's life easier.
  This wrapper checks for `$POTDOMAIN` construction variable (or override in
  `**kw`) and treats it appropriatelly. 
  """
  if source is _null:
    if 'POTDOMAIN' in kw:
      domain = kw['POTDOMAIN']
    elif 'POTDOMAIN' in env:
      domain = env['POTDOMAIN']
    else:
      domain = 'messages'
    source = [ domain ] # NOTE: Suffix shall be appended automatically
  return env._POInitBuilder(target, source, **kw)