 literal data...|
            +---+---+---+---+================================+

         LEN is the number of data bytes in the block.  NLEN is the
         one's complement of LEN.

      3.2.5. Compressed blocks (length and distance codes)

         As noted above, encoded data blocks in the "deflate" format
         consist of sequences of symbols drawn from three conceptually
         distinct alphabets: either literal bytes, from the alphabet of
         byte values (0..255), or &lt;length, backward 