Source

File: wp-includes/widgets/class-wp-widget-media-gallery.php

public function get_instance_schema() {
		$schema = array(
			'title'          => array(
				'type'                  => 'string',
				'default'               => '',
				'sanitize_callback'     => 'sanitize_text_field',
				'description'           => __( 'Title for the widget' ),
				'should_preview_update' => false,
			),
			'ids'            => array(
				'type'              => 'array',
				'items'             => array(
					'type' => 'integer',
				),
				'default'           => array(),
				'sanitize_callback' => 'wp_parse_id_list',
			),
			'columns'        => array(
				'type'    => 'integer',
				'default' => 3,
				'minimum' => 1,
				'maximum' => 9,
			),
			'size'           => array(
				'type'    => 'string',
				'enum'    => array_merge( get_intermediate_image_sizes(), array( 'full', 'custom' ) ),
				'default' => 'thumbnail',
			),
			'link_type'      => array(
				'type'                  => 'string',
				'enum'                  => array( 'post', 'file', 'none' ),
				'default'               => 'post',
				'media_prop'            => 'link',
				'should_preview_update' => false,
			),
			'orderby_random' => array(
				'type'                  => 'boolean',
				'default'               => false,
				'media_prop'            => '_orderbyRandom',
				'should_preview_update' => false,
			),
		);

		/** This filter is documented in wp-includes/widgets/class-wp-widget-media.php */
		$schema = apply_filters( "widget_{$this->id_base}_instance_schema", $schema, $this );

		return $schema;
	}