Additional per-sequence information can be placed in a header before
any blocks appear. These lines, one per sequence and in exactly the
same order as the sequences appear in the alignment, are formatted
like #=SQ <seqname> <weight> <database source name> <database
accession> <source coordinates as start..stop::original length>
<description>.
This information includes a sequence weight (for compensating for biased representation of subfamilies of sequences in the alignment); source information, if the sequence came from a database, consisting of identifier, accession number, and source coordinates; and a description of the sequence.
If a #=SQ line is present, all the fields must be present on
each line and one #=SQ line must be present for each sequence.
If no information is available for a field, use '-' for all the fields
except the source coordinates, which would be given as '0'.