docs: def remove_empty_cols(records):
      """Remove all-gap columns from aligned SeqRecords."""
      # In case it's a generator, turn it into a list
      records = list(records)
      seqstrs = [str(rec.seq) for rec in records]
      clean_cols = [col
                    for col in zip(*seqstrs)
                    if not all(c == '-' for c in col)]
      clean_seqs = [''.join(row)
                    for row in zip(*clean_cols)]
      for rec, clean_seq in zip(records, clean_seqs):
          yield SeqRecord(Seq(clean_seq, rec.seq.alphabet), id=rec.id,
                          name=rec.name, description=rec.description,
                          dbxrefs=rec.dbxrefs, features=rec.features,
                          annotations=rec.annotations,
                          letter_annotations=rec.letter_annotations)