'Get all tags in this handler, regardless of category.
Args:
return_key_and_category (bool, optional): Return a list of
tuples `[(key, category), ...]`.
Returns:
tags (list): A list of tag keys `[tagkey, tagkey, ...]` or
a list of tuples `[(key, category), ...]` if
`return_key_and_category` is set.'

def all(self, return_key_and_category=False):

    if (not self._cache_complete):
        self._fullcache()
    tags = sorted(self._cache.values())
    if return_key_and_category:
        return [(to_str(tag.db_key), to_str(tag.db_category)) for tag in tags]
    else:
        return [to_str(tag.db_key) for tag in tags]
