Internal inconsistency wrt year 0000

The inconsistency between XML Schema Part 2 and ISO 8601:2000 wrt year 0000 
has already been commented on, but there is also a minor internal 
inconsistency.  XML Schema Part 2 disallows year 0000, which means that 
year -0001 corresponds to 1BC (whereas in ISO 8601:2000, 1BC is year 0000). 
Now the year 1BC in the proleptic Gregorian calendar is a leap year. 
However, appendix E uses the formula

  modulo(Y, 400) = 0 OR (modulo(Y, 100) != 0) AND modulo(Y, 4) = 0

to determine whether Y is a leap year.  But this formula makes year -0001 
not a leap year.  If year 0000 was allowed (representing 1BC), then the 
formula would be correct.

James