thank you for your help. Somehow though, when running a transformation on your modified sample, the output came up empty.
Changing the root map to any of the submaps containing the reference to "topicKeys.ditamap" didn’t help.
Could it be that once the publishing engine sees a .ditaval it will attempt to do its branch filtering but will pretty much abort the entire process in the absence of a direct topicref?
In any case, the processing order of the publishing engine seems to forbid the combination of branch-filtering and keyrefs, which I find a pity.
Or am I missing something?