[BioPython] modified nucleotides

[Christoph Wierling]

Hi there,
   I think, for some reasons it may be necessary to know if a DNA- or
RNA-nucleotide of a sequence is modified e.g. by methylation.
Obviously the IUPAC does not give any suggestions, but I think it should
be take into consideration how to describe modifications like
N6-methyladenosine, 5-methylcytosine, or N4-methylcytosine in
DNA-sequences (e.g. in any derivation of the Alphabet class).

Christoph.