lter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'] );
		}
	}

	if ( isset( $args['auth_callback'] ) && is_callable( $args['auth_callback'] ) ) {
		if ( ! empty( $object_subtype ) ) {
			remove_filter( "auth_{$object_type}_meta_{$meta_key}_for_{$object_subtype}", $args['auth_callback'] );
		} else {
			remove_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'] );
		}
	}

	unset( $wp_meta_keys[ $object_type ][ $object_subtype ][ $meta_key ] );

	// Do some clean up.
	if ( empty( $wp_meta_keys[ $object_type ][ $object_subtype ] ) ) {
		unset( $wp_meta_keys[ $object_type ][ $object_subtype ] );
	}
	if ( empty( $wp_meta_keys[ $object_type ] ) ) {
		unset( $wp_meta_keys[ $object_type ] );
	}

	return true;
}

/**
 * Retrieves a list of registered metadata args for an object type, keyed by their meta keys.
 *
 * @since 4.6.0
 * @since 4.9.8 The `$object_subtype` parameter was added.
 *
 * @param string $object_type    Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
 *                               or any other object type with an associated meta table.
 * @param string $object_subtype Optional. The subtype of the object type. Default empty string.
 * @return array[] List of registered metadata args, keyed by their meta keys.
 */
function get_registered_meta_keys( $object_type, $object_subtype = '' ) {
	global $wp_meta_keys;

	if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys[ $object_type ] ) || ! isset( $wp_meta_keys[ $object_type ][ $object_subtype ] ) ) {
		return array();
	}

	return $wp_meta_keys[ $object_type ][ $object_subtype ];
}

/**
 * Retrieves registered metadata for a specified object.
 *
 * The results include both meta that is registered specifically for the
 * object's subtype and meta that is registered for the entire object type.
 *
 * @since 4.6.0
 *
 * @param string $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
 *                            or any other object type with an associated meta table.
 * @param int    $object_id   ID of the object the metadata is for.
 * @param string $meta_key    Optional. Registered metadata key. If not specified, retrieve all registered
 *                            metadata for the specified object.
 * @return mixed A single value or array of values for a key if specified. An array of all registered keys
 *               and values for an object ID if not. False if a given $meta_key is not registered.
 */
function get_registered_metadata( $object_type, $object_id, $meta_key = '' ) {
	$object_subtype = get_object_subtype( $object_type, $object_id );

	if ( ! empty( $meta_key ) ) {
		if ( ! empty( $object_subtype ) && ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
			$object_subtype = '';
		}

		if ( ! registered_meta_key_exists( $object_type, $meta_key, $object_subtype ) ) {
			return false;
		}

		$meta_keys     = get_registered_meta_keys( $object_type, $object_subtype );
		$meta_key_data = $meta_keys[ $meta_key ];

		$data = get_metadata( $object_type, $object_id, $meta_key, $meta_key_data['single'] );

		return $data;
	}

	$data = get_metadata( $object_type, $object_id );
	if ( ! $data ) {
		return array();
	}

	$meta_keys = get_registered_meta_keys( $object_type );
	if ( ! empty( $object_subtype ) ) {
		$meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $object_type, $object_subtype ) );
	}

	return array_intersect_key( $data, $meta_keys );
}

/**
 * Filters out `register_meta()` args based on an allowed list.
 *
 * `register_meta()` args may change over time, so requiring the allowed list
 * to be explicitly turned off is a warranty seal of sorts.
 *
 * @access private
 * @since 5.5.0
 *
 * @param array $args         Arguments from `register_meta()`.
 * @param array $default_args Default arguments for `register_meta()`.
 * @return array Filtered arguments.
 */
function _wp_register_meta_args_allowed_list( $args, $default_args ) {
	return array_intersect_key( $args, $default_args );
}

/**
 * Returns the object subtype for a given object ID of a specific type.
 *
 * @since 4.9.8
 *
 * @param string $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
 *                            or any other object type with an associated meta table.
 * @param int    $object_id   ID of the object to retrieve its subtype.
 * @return string The object subtype or an empty string if unspecified subtype.
 */
function get_object_subtype( $object_type, $object_id ) {
	$object_id      = (int) $object_id;
	$object_subtype = '';

	switch ( $object_type ) {
		case 'post':
			$post_type = get_post_type( $object_id );

			if ( ! empty( $post_type ) ) {
				$object_subtype = $post_type;
			}
			break;

		case 'term':
			$term = get_term( $object_id );
			if ( ! $term instanceof WP_Term ) {
				break;
			}

			$object_subtype = $term->taxonomy;
			break;

		case 'comment':
			$comment = get_comment( $object_id );
			if ( ! $comment ) {
				break;
			}

			$object_subtype = 'comment';
			break;

		case 'user':
			$user = get_user_by( 'id', $object_id );
			if ( ! $user ) {
				break;
			}

			$object_subtype = 'user';
			break;
	}

	/**
	 * Filters the object subtype identifier for a non-standard object type.
	 *
	 * The dynamic portion of the hook name, `$object_type`, refers to the meta object type
	 * (post, comment, term, user, or any other type with an associated meta table).
	 *
	 * Possible hook names include:
	 *
	 *  - `get_object_subtype_post`
	 *  - `get_object_subtype_comment`
	 *  - `get_object_subtype_term`
	 *  - `get_object_subtype_user`
	 *
	 * @since 4.9.8
	 *
	 * @param string $object_subtype Empty string to override.
	 * @param int    $object_id      ID of the object to get the subtype for.
	 */
	return apply_filters( "get_object_subtype_{$object_type}", $object_subtype, $object_id );
}