fn:sum

Returns the total of a sequence of numbers or durations.

sum($arg as xs:anyAtomicType*) ➔ xs:anyAtomicType

Arguments
	$arg	xs:anyAtomicType*	The sequence of values to be totalled
Result		xs:anyAtomicType

sum($arg as xs:anyAtomicType*, $zero as xs:anyAtomicType?) ➔ xs:anyAtomicType?

Arguments
	$arg	xs:anyAtomicType*	The sequence of values to be totalled
	$zero	xs:anyAtomicType?	The value to return if the input sequence is empty (default integer zero)
Result		xs:anyAtomicType?

http://www.w3.org/2005/xpath-functions