WordPress at a glance
function is not described

filter_default_metadata() WP 5.5.0

Filters into default_{$object_type}_metadata and adds in default value.

No Hooks.

Return

Mixed. Single metadata default, or array of defaults.

Usage

filter_default_metadata( $value, $object_id, $meta_key, $single, $meta_type );
$value(mixed) (required)
Current value passed to filter.
$object_id(int) (required)
ID of the object metadata is for.
$meta_key(string) (required)
Metadata key.
$single(true|false) (required)
If true, return only the first value of the specified meta_key. This parameter has no effect if meta_key is not specified.
$meta_type(string) (required)
Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user', or any other object type with an associated meta table.

Changelog

Since 5.5.0 Introduced.

Code of filter_default_metadata() WP 5.7.2

<?php
function filter_default_metadata( $value, $object_id, $meta_key, $single, $meta_type ) {
	global $wp_meta_keys;

	if ( wp_installing() ) {
		return $value;
	}

	if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys[ $meta_type ] ) ) {
		return $value;
	}

	$defaults = array();
	foreach ( $wp_meta_keys[ $meta_type ] as $sub_type => $meta_data ) {
		foreach ( $meta_data as $_meta_key => $args ) {
			if ( $_meta_key === $meta_key && array_key_exists( 'default', $args ) ) {
				$defaults[ $sub_type ] = $args;
			}
		}
	}

	if ( ! $defaults ) {
		return $value;
	}

	// If this meta type does not have subtypes, then the default is keyed as an empty string.
	if ( isset( $defaults[''] ) ) {
		$metadata = $defaults[''];
	} else {
		$sub_type = get_object_subtype( $meta_type, $object_id );
		if ( ! isset( $defaults[ $sub_type ] ) ) {
			return $value;
		}
		$metadata = $defaults[ $sub_type ];
	}

	if ( $single ) {
		$value = $metadata['default'];
	} else {
		$value = array( $metadata['default'] );
	}

	return $value;
}