BSA — The spec mentions IUPAC-IUB single letter codes

The spec mentions IUPAC-IUB single letter codes,

I think this has been renamed to IUPAC-IUBMB Joint Commission on
Biochemical Nomenclature (JCBN); the best web site for this is

http://www.chem.qmw.ac.uk/iupac/AminoAcid/ (amino acids)
http://www.chem.qmw.ac.uk/iubmb/misc/naseq.html (nucleic acids)

http://www.chem.qmw.ac.uk/iubmb/nomenclature/ (all biostandards)

Might be useful to include in the references.

IUB allows termination characters in amino acids; I think we should not
allow them. Also, it might be good to explicitly state that gap characters
('-' or so) are not supposed to be in sequences (this is fairly implicit in
IUPAC, so I think had doesn't hurt to be clear about this).

accepted