There can be no spaces in the label though the sequence itself can be
formatted into blocks using multiple lines and spaces. An alternate way
of specifying the sequences is using the interleaved format. This enables
the sequences to be split into homologous blocks. The non-interleaved example
given above could equivalently be written:
2 8 DNA
Notice that only the first interleaved block should contain labels. Subsequent interleaved blocks are assumed to have the same labels and to be in the same order.