wp-includes/meta.php:1584Filters into default_{$object_type}_metadata and adds in default value.
$valuemixed$object_idint$meta_keystring$singlebool$meta_typestringmixedfunction 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;}Introduced in 5.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/meta.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.