* 'inventory_presser_make' becomes 'make'. Careful to not damage any
	 * provided key that does not start with our prefix.
	 *
	 * @param  string $meta_key The prefixed meta key.
	 * @return string The un-prefixed meta key.
	 */
	public static function untranslate_custom_field_names( $meta_key ) {
		if ( empty( $meta_key ) ) {
			return '';
		}
		$meta_key = strtolower( $meta_key );
		// prefix may start with an underscore because previous versions hid some meta keys.
		$prefix = ( '_' === $meta_key[0] ? '_' : '' ) . self::meta_prefix();

		// does $meta_key actually start with the $prefix?
		if ( substr( $meta_key, 0, strlen( $prefix ) ) === $prefix ) {
			// remove the prefix.
			return substr( $meta_key, strlen( $prefix ) );
		}

		return $meta_key;
	}

	/**
	 * If no parameter is provided, returns an array containing lowercase
	 * weekdays as keys and title case, three-letter abbreviations as values.