Currently, the listing contains the Courant and Fourier numbers for the momentum equation, and the combined Courant/Fourier criterion. It could be interesting to also have this combined Courant/Fourier criterion for transported scalars. This might be especially relevant for buoyant scalars.

someone writing a custom sender, creates a do_send or some such plugin, it has a hard-coded destination, so destination is not a useful setting.
however sr_sender has a hard coded check where it refuses to start unless destination is set and valid.
The requirement forced the user to assign a fake destination, and the fake destination had to have a valid entry in credentials.conf. ... it might