public function op($operation)
    {
        if (!$operation) {
            return $this;
        }
        $result = clone $this;
        $result->operations[]['custom'] = $operation;
        return $result;
    }
public function op($operation)
    {
        if (!$operation) {
            return $this;
        }
        $result = clone $this;
        $result->operations[]['custom'] = $operation;
        return $result;
    }
public function op ( $ operation ) { if ( ! $ operation ) { return $ this ; } $ result = clone $ this ; $ result -> operations [ ] [ 'custom' ] = $ operation ; return $ result ; }
Add any custom operation.

@param string $operation
@return File
Add any custom operation .