public function modify(string $specification) : self
    {
        $instance = clone $this;
        
        $instance->date->modify($specification);
        
        return $instance;
    }
public function modify(string $specification) : self
    {
        $instance = clone $this;
        
        $instance->date->modify($specification);
        
        return $instance;
    }
public function modify ( string $ specification ) : self { $ instance = clone $ this ; $ instance -> date -> modify ( $ specification ) ; return $ instance ; }
Creates a new instance modified according to the specification.

For valid formats @see http://php.net/manual/en/datetime.formats.relative.php

@param string $specification

@return self
Creates a new instance modified according to the specification .