FAST specification, in the item 10.7.3 ASCII String Delta, says:

The delta value is represented as a Signed Integer subtraction length followed by […].

The item 10.6.1.1 Signed Integer says:

The entity value is a two’s complement integer representation […]

But the Appendix 3.2.5 FAST v1.1 Delta Operator Examples, EXAMPLE 4 uses a negative zero.

The problem is: There is no negative zero in two’s complement integer representation. There is only zero.

Can anyone help me understand this? The example seems to use something other than two’s complement. For instance, -2 in twos complement should be 1…110, the example represents -2 as 1…1101 that is actually -3 in twos complement.