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function is not described

rest_filter_response_fields() WP 4.8.0

Filter the API response to include only a white-listed set of response object fields.

No Hooks.

Return

WP_REST_Response. Response to be served, trimmed down to contain a subset of fields.

Usage

rest_filter_response_fields( $response, $server, $request );
$response(WP_REST_Response) (required)
Current response being served.
$server(WP_REST_Server) (required)
ResponseHandler instance (usually WP_REST_Server).
$request(WP_REST_Request) (required)
The request that was used to make current response.

Code of rest filter response fields: wp-includes/rest-api.php VER 5.1.1

<?php
function rest_filter_response_fields( $response, $server, $request ) {
	if ( ! isset( $request['_fields'] ) || $response->is_error() ) {
		return $response;
	}

	$data = $response->get_data();

	$fields = wp_parse_list( $request['_fields'] );

	if ( 0 === count( $fields ) ) {
		return $response;
	}

	// Trim off outside whitespace from the comma delimited list.
	$fields = array_map( 'trim', $fields );

	$fields_as_keyed = array_combine( $fields, array_fill( 0, count( $fields ), true ) );

	if ( wp_is_numeric_array( $data ) ) {
		$new_data = array();
		foreach ( $data as $item ) {
			$new_data[] = array_intersect_key( $item, $fields_as_keyed );
		}
	} else {
		$new_data = array_intersect_key( $data, $fields_as_keyed );
	}

	$response->set_data( $new_data );

	return $response;
}