2.64.4.1 Aggregate Function: Sum

The following are the arguments, types, and specification of the Sum aggregate function.

Function	Arguments	Type	Specification
Sum	Return	*	The sum of the non-null values of the items.  Return type is the same as the Items.
	Items	Numeric	The set of items to sum.

The value of the Items argument MUST NOT be a literal set, that is, the Items argument MUST NOT be a Literal element with a Literal.Values child element.