
The number function converts its argument to a number as follows:

A string that consists of decimal number and optional whitespaces is converted to the number recorded.
Any other string is converted to NaN ("not-a-number" value).
More precisely,
a string that consists of
optional whitespace followed by an optional plus or minus sign
followed by a Number followed by whitespace is converted to the
IEEE 754 number that is nearest
(according to the IEEE 754 round-to-nearest rule)
to the mathematical value represented by the string.
Note that it differs from XPATH 1.0 standard where plus sign is not allowed
before Number part of the string.

Boolean true is converted to 1; boolean false is converted to 0.

A node-set is first converted to a string as if by a call to the string function and then converted in the same way as a string argument.

An object of a type other than the four basic types is converted to a number in a way that is dependent on that type.

If the argument is omitted, it defaults to a node-set with the context node as its only member.
