Is it an oversight that the expression maps dialog does not allow negative relative channel change?

As title.

Actually I’ve found out that putting 0 to the relative channel switch goes up one channel!

It wasn’t an intentional limitation - I think it’s just the default range of the spinbox doesn’t allow it to go negative. I’ll see if I can fix this for a future release. What is the specific use case you have? Normally the idea is that the base ‘natural’ patch is on one channel and then other techniques are on subsequent channels.

Thanks for the clarification. I guess with negative change I can go back to the base patch without using the absolute channel change.

Not necessarily. The relative changes aren’t cumulative - they are relative to the channel used for ‘nat’, not for the last channel. So a typical scenario might be this (eg for EW Hollywood Strings):

Instruments loaded in plugin
ch1 default sustaining/long/arco patch
ch2 pizz
ch3 staccato

In the expression map you would create this:
nat | absolute channel = 1
pizz | relative channel = 1 (relative to ch1 => ch2)
stacc | relative channel = 2 (relative to ch1 => ch3)

Great! Thanks Paul.