/**
* Specify $elemMatch criteria for the current field.
*
* You can create a new expression using the {@link Builder::expr()} method.
*
* @see Expr::elemMatch()
* @see http://docs.mongodb.org/manual/reference/operator/elemMatch/
* @param array|Expr $expression
* @return self
*/
public function elemMatch($expression)
{
$this->expr->elemMatch($expression);
return $this;
}