Source

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

public function get_instance_schema() {
		$schema = array(
			'attachment_id' => array(
				'type'        => 'integer',
				'default'     => 0,
				'minimum'     => 0,
				'description' => __( 'Attachment post ID' ),
				'media_prop'  => 'id',
			),
			'url'           => array(
				'type'        => 'string',
				'default'     => '',
				'format'      => 'uri',
				'description' => __( 'URL to the media file' ),
			),
			'title'         => array(
				'type'                  => 'string',
				'default'               => '',
				'sanitize_callback'     => 'sanitize_text_field',
				'description'           => __( 'Title for the widget' ),
				'should_preview_update' => false,
			),
		);

		/**
		 * Filters the media widget instance schema to add additional properties.
		 *
		 * @since 4.9.0
		 *
		 * @param array           $schema Instance schema.
		 * @param WP_Widget_Media $this   Widget object.
		 */
		$schema = apply_filters( "widget_{$this->id_base}_instance_schema", $schema, $this );

		return $schema;
	}