public function at($start = null, $length = null)
    {
        return new String(mb_substr((string) $this, $start, $length, 'UTF-8'));
    }
public function at($start = null, $length = null)
    {
        return new String(mb_substr((string) $this, $start, $length, 'UTF-8'));
    }
public function at ( $ start = null , $ length = null ) { return new String ( mb_substr ( ( string ) $ this , $ start , $ length , 'UTF-8' ) ) ; }
Returns part of a string

@param integer start
@param  integer   $length the length of the string from the starting point
@return PO\String
Returns part of a string