':param fileids: a list or regexp specifying the fileids that have to be
returned as a raw string.
:return: the given file(s) as a single string.
:rtype: str'

def raw(self, fileids=None):

    if (fileids is None):
        fileids = self._fileids
    elif isinstance(fileids, string_types):
        fileids = [fileids]
    return concat([self.open(f).read() for f in fileids])
