@classmethod
def make_category_tag(cls, category, value=None, tag_prefix=None, value_sep
    =None):
    """Build category tag (mostly for testing purposes).
        :return: Category tag as string (without leading AT char).
        """
    if tag_prefix is None:
        tag_prefix = cls.tag_prefixes[0]
    if value_sep is None:
        value_sep = cls.value_separator
    value = value or ''
    return '%s.with_%s%s%s' % (tag_prefix, category, value_sep, value)
