[F&O] op:to doesn't match language specification

In the October 04 language specification op:to was changed to have 
optionally have empty operands:
"Each of the operands of the to operator is converted as though it was 
an argument of a function with the expected parameter type xs:integer?. 
If either operand is an empty sequence, or if the integer derived from 
the first operand is greater than the integer derived from the second 
operand, the result of the range expression is an empty sequence..."

Which means in F&O the signature
op:to($firstval as xs:integer, $lastval as xs:integer) as xs:integer*

should be:
op:to($firstval as xs:integer?, $lastval as xs:integer?) as xs:integer*

--Sarah