code: public static function generate_ID( $type, $item ) {
  
  		$item = self::sanitize_item( $item );
  		$type = in_array( $type, array( 'comment', 'post' ) )
  			? $type
  			: 'post';
  		$blog_ID = get_current_blog_ID();
  		$base = array(
  			$type,
  			$blog_ID,
  			$item->ID,
  			$item->date_gmt
  		);
  		$url_parts = parse_url( get_option( 'siteurl' ) );
  
  		$ID = sha1( implode( ':', $base ) ) . '@' . $url_parts[ 'host' ];
  
  		return $ID;
  	}
docs: generates the ID based on content type (comment or post)
  
  @param string $type
  @param object $item