Returns the arithmetic sum of its operands: ($arg1 + $arg2).
op:numeric-add( $arg1 as xs:numeric,$arg2 as xs:numericxs:numericGeneral rules: see .
 For xs:float or xs:double values, if one of the operands is a
            zero or a finite number and the other is INF or -INF,
               INF or -INF is returned. If both operands are
               INF, INF is returned. If both operands are
               -INF, -INF is returned. If one of the operands is
               INF and the other is -INF, NaN is
            returned.