The final piece of a BPL file is the postamble. It has two components:
(fontbb llx lly urx ury). Defines the
bounding box for the entire font in the same way as the bb
property defines the bounding box for a character. See section 12.1.2 BPL characters.
(nchars unsigned). The number of characters in the BPL
file. This is purely for informational purposes; BPLtoBZR ignores it.