Is there any documentation concerning the syntax and schema for the upgrade instructions xml file for an addon?
Yes:
@laursen many thanks for this. Unfortunately it confirms what I feared: the upgrade syntax only allows to update the channels of a given thing-type-uid … whereas I probably need a mechanism to upgrade the channels of many (perhaps dynamically defined) thing-type-uid’s which have (perhaps dynamically defined) channels of a given channel-type-uid. i.e. to update the channels of any wild card thing-type-uid that implements a given channel-type-uid