The caravel frame for GF180 currently has a lot of labels on the GDS layers 21/10 and 204/10 for gf180mcuC, but those layers do not exist in the documentation. So I think we should either remove the layers from the Caravel design, or we should filter them out from the tapeout (perhaps the layers help during design), so that we deliver GDS as clean as possible to GF. Or does anyone need those layers to be present in the tapeout files?

Those are text layers for nwell and pwell; I added them so that the ports for the nwell and substrate bias could be added on the correct layers in the GDS views of the standard cells, since those layers only connect up to metal in the tap cells. The usage is straightforward: The layer is the same layer (nwell or pwell), and the purpose is the standard pin purpose. The submission form for GF allows one to specify user layers to be ignored, but if not, it is only flagged as a warning by GF.

Then I would suggest that we filter them out automatically right before the tapeout, to ease the tapeout review process

That's our problem, not yours. It would not be a good idea to remove those layers at any time before final submission to GF, since otherwise there will be issues with the standard cell ports when reading back the GDS and trying to do an extraction from it.

Should I add those labels into standard cells I generate too?