public function exnor($value) {


        if($this->value !== null){
            return $this->markErrorIf($value === null);
        }
        if($value !== null){

            return $this->markErrorIf($this->value === null, false);
        }
        return $this;
    }
public function exnor($value) {


        if($this->value !== null){
            return $this->markErrorIf($value === null);
        }
        if($value !== null){

            return $this->markErrorIf($this->value === null, false);
        }
        return $this;
    }
public function exnor ( $ value ) { if ( $ this -> value !== null ) { return $ this -> markErrorIf ( $ value === null ) ; } if ( $ value !== null ) { return $ this -> markErrorIf ( $ this -> value === null , false ) ; } return $ this ; }
Verify the value and given value are both not null or both null.
@param $value
Verify the value and given value are both not null or both null .