system/Database/Schema/ColumnDefination.php
/**
     * Specify the referenced column
     *
     * @param string $column
     * @return \System\Database\Schema\ColumnDefination
     */
Specify the referenced column
@param string $column
@return \System\Database\Schema\ColumnDefination
Specify the referenced column @param string $column @return \ System \ Database \ Schema \ ColumnDefination
public function on(string $column)
    {
        self::$migration .= "`$column`), ";
        return $this;
    }
public function on ( string $ column ) { self :: $ migration .= " ` $ column `),  " ; return $ this ; }
Specify the referenced column
 @param string $column
 @return \System\Database\Schema\ColumnDefination
Specify the referenced column @param string $column @return \ System \ Database \ Schema \ ColumnDefination