The operators + and - perform addition and subtraction of numbers,
in the usual way. If the operands are of different types, one of them is promoted, and the result
is the same type as the operands after promotion. For example, adding two integers produces
an integer; adding an integer to a double produces a double.
Note that the - operator may need to be preceded by a space to prevent it being
parsed as part of the preceding name.
XPath 2.0 also allows these operators to be used for adding durations to durations or to dates and times.
