/**
* Add an $or clause to the current query.
*
* You can create a new expression using the {@link Builder::expr()} method.
*
* @see Expr::addOr()
* @see http://docs.mongodb.org/manual/reference/operator/or/
* @param array|Expr $expression
* @return self
*/
public function addOr($expression)
{
$this->expr->addOr($expression);
return $this;
}