Correspondence between PDB chain/residue identifiers and `bb.annotate()` output

[cgoliver]

Thank you for this very useful library.

Just would like a bit more detail on the output of bb.annotate() and how it matches to the original PDB's residue and chain identifies. i.e. I would like to be able to map the annotate output back to the original PDB.

I noticed that the chains are relabeled to have integer IDs (this seems to be coming from the way mdtraj handles pdbs). Now mdtraj seems to be preserving the original chain IDs (https://github.com/mdtraj/mdtraj/pull/1715) I'm investigating whether this can be added as a feature to this project.

Do the residue positions also get relabeled or do these correspond to the original PDB?

Thanks!