
This function calculates values of its arguments, from left to right.
If the value of calculated parameter is true, the function returns true immediately,
without calculating of the remaining parameters.
If the list of arguments ends without any true value calculated, the function
returns false (Thus it returns true when called without arguments).

The name of this function is the same as name of "or" XPATH and XQUERY operator.
Thus it must be surronded bu double quotes when used in XPATH or XQUERY expressions.
Moreover, this function is not a part of XPATH standard, so it cannot be used if
portability is important.
