Why is there anexpression error here? I would expect that the expression number(-10000101) evaluates to a negative number taking part in the comparsion. It looks as if the minus sign is not seen as an unary minus, while -10000101 should have be evaluated by Lua's tonumber(-10000101).

relevant code snippet is:
\xmlfilter{#1}{lpath[number(@date) <= number(-10000101)]/command(...)

xml > lpath > error in expression: number(@date) <= number(-10000101) => expr.number((ll.at and ll.at['date'])) <= expr.number(expr.child(ll,'-')10000101)

Changing number(-10000101) to -10000101 does not make a difference. 
The @date attribute has no problem with a negative value.

Hans van der Meer