[GRASS5] Label only some features in vector map?

Hi,
   I'm starting to develop an application that will be connected to grass. Now, I have to label only some features from a vector map.

   I read the programming manual, but i didn't find any function that let me do this. Anybody knows how to do it?

   I've also tried to call (from my program) executables's grass which labels vector maps, but they label all the features in the map.

   I can't use a mask, because the set of features changes in a dynamic way, so i should have a mask for every combination of features.

Thanks very much in advance.

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