The parser relies on the system call, strtod(), to parse a string representation
of a double/float data. In the case of no invalid characters found, the strtod()
returns a double/float value if it is representable on that platform, or raises
ERANGE to indicate either underflow or underflow occurs. And the parser assigns
zero to the said data if underflow is found.
The threshold, where the strtod() decides if an underflow occurs, varies on
platforms. On Windows, it is roughly the order of e-308, on Linux, e-325, and
on AIX, HP-UX and Solaris, e-324.
So in an instance document, a data of value 1.0e-310 from a type with minExclusive 0,
is considered invalid on windows (since it is converted to 0 and therefore violates
the minExclusive constraint), but valid on other Unix platforms (since it remains
the original value).
The discussion above applies to data in xsd file as well.