Dorico 3 relative channel switching?

So, how is this feature meant to be applied?

Suppose I have a divisi section, and in my VST plug-in, I’ve got four samples loaded: MIDI channels 1 and 2 are meant for the upper divisi staff, and MIDI channels 3 and 4 are meant for the lower divisi staff. Channels 1 and 3 represent numerous keyswitched samples, and channels 2 and 4 represent samples that are not available among the keyswitched sounds.

I understand defining a relative switch in the expression map editor to effect a change from channel 1 to 2, and from channel 3 to 4, but how do I instruct the divisi staves to get back to their respective channels of 1 and 3? Obviously, I can’t use absolute channel changes, because that would cause either the upper or lower divisi staff to employ the same channel as the other staff.

‘Relative’ here means relative to the ‘base’ channel, ie the channel you set in the track header. They’re not cumulative. So in most cases you’d probably want to set your ‘natural’ switch to have a relative channel of 0. eg

natural: Relative channel 0
pizz: Relative channel 1

Brilliant. Thanks, Dr. Walmsley!

this should be in the manual. Took me a while to find this post but it’s worked great for me too!