code: public function where($exp, $bind = false) 
  	{
  		return $this->appendPart(CmdUpdate::PART_WHERE, $exp, $bind); 
  	}
docs: Add additional where clause.
  @param string $exp Expression to append.
  @param mixed|array|null $bind Single bind value, array of values or false if no
  bind values are needed for this expression.
  @return static