According to XML Schema Part 2: Datatypes Second Edition; 3.2.7 dateTime:

"Local" or untimezoned times are presumed to be the time in the timezone of some unspecified locality as prescribed by the appropriate legal authority; currently there are no legally prescribed timezones which are durations whose magnitude is greater than 14 hours.

And in 3.2.7.3 Timezones:

Timezones are durations with (integer-valued) hour and minute properties (with the hour magnitude limited to at most 14, and the minute magnitude limited to at most 59, except that if the hour magnitude is 14, the minute value must be 0); they may be both positive or both negative. 

However, the file xmlschemastypes.c contains the line:

#define VALID_TZO(tzo)          ((tzo > -840) && (tzo < 840))

which constrains the valid timzone to not include -14:00 and 14:00.  (840 is 14:00).

Then in 3.2.1.7:

hh is a two-digit numeral that represents the hour; '24' is permitted if the minutes and seconds represented are zero, and the dateTime value so represented is the first instant of the following day (the hour property of a dateTime object in the ·value space· cannot have a value greater than 23);

In section 3.2.8 time, it refers to the appendix paragraph D, ISO 8601 Date and Time Formats (§D).  In that section, it reads:

h -- represents a digit used in the time element "hour". The two digits in a hh format can have values from 0 to 24. If the value of the hour element is 24 then the values of the minutes element and the seconds element must be 00 and 00. 

The file xmlschemastypes.c does not take this exception into account, but has:

#define VALID_HOUR(hr)          ((hr >= 0) && (hr <= 23))


That same appendix explains:

s -- represents a digit used in the time element "second". The two digits in a ss format can have values from 0 to 60. In the formats described in this specification the whole number of seconds ·may· be followed by decimal seconds to an arbitrary level of precision. This is represented in the picture by "ss.sss". A value of 60 or more is allowed only in the case of leap seconds. 

However, the same LIBXML2 file xmlschemastypes.c contains:

#define VALID_SEC(sec)          ((sec >= 0) && (sec < 60))

There is further text in this appendix which might be useful to the developer.  It may be found at: http://www.w3.org/TR/xmlschema-2/#isoformats


As a result, LIBXML2 fails to validate the legal "dateTime" and "time" values of 2010-12-31T23:59:60 and 24:00:00 and 12:00:00+14:00.