def extract_metadata_value(metadata_value):
    """Converts a lxml.objectify.ObjectifiedElement metadata value to a string.

    The textual representation of the metadata value is extracted out of the
    metadata value object.

    :param lxml.objectify.ObjectifiedElement metadata_value: an object
        containing EntityType.METADATA_VALUE XML data.

    :return: string representation of the metadata value

    :rtype: str
    """
    return metadata_value.TypedValue.Value.text
