code: public function where($key, $operator, $value=null, $boolean=Queryable::AND_)
      {
          $this->criteria->where($key, $operator, $value, $boolean);
          return $this;
      }
docs: {@inheritdoc} Forwards to criteria returns itself
  
  @param string $key
  @param string $operator
  @param mixed $value
  @param string $boolean
  @return self