code: public function write_data() {
  		$option_key = "_wp_session_{$this->session_id}";
  		// Only write the collection to the DB if it's changed.
  		if ( $this->dirty ) {
  			if ( false === get_option( $option_key ) ) {
  				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
  				add_option( "_wp_session_expires_{$this->session_id}", $this->expires, '', 'no' );
  			} else {
  				delete_option( "_wp_session_{$this->session_id}" );
  				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
  			}
  		}
  	}
docs: Write the data from the current session to the data storage system.