Is there an AnchorHub tag, 'tag', registered for file 'file_key' in
        'anchors'?

        :param anchors: Dictionary mapping string file paths to inner
            dictionaries. These inner dictionaries map string AnchorHub tags
            to string generated anchors
        :param file_key: The absolute path to the file that may or may not
            have the AnchorHub tag in it. Used as a key to anchors
        :param tag: The string being tested
        :return: True if tag is a valid AnchorHub tag in the file associated
            with 'file_key'

def _file_has_tag_anchor_keypair(self, anchors, file_key, tag):
        """
        Is there an AnchorHub tag, 'tag', registered for file 'file_key' in
        'anchors'?

        :param anchors: Dictionary mapping string file paths to inner
            dictionaries. These inner dictionaries map string AnchorHub tags
            to string generated anchors
        :param file_key: The absolute path to the file that may or may not
            have the AnchorHub tag in it. Used as a key to anchors
        :param tag: The string being tested
        :return: True if tag is a valid AnchorHub tag in the file associated
            with 'file_key'
        """
        return file_key in anchors and tag in anchors[file_key]