-reads a GNU Unifont .hex file from stdin and prints a 16 by 16 grid of the
-number of defined code points in each 256 character block to stdout.
-Code points proceed from left to right, then top to bottom.
-.PP
+reads a GNU Unifont .hex file from STDIN and prints a 16 by 16 grid of the
+number of defined code points in each 256 character block within a Unicode
+plane to STDOUT. Code points proceed from left to right, then top to bottom.
+In all planes, code points U+*FFFE and U+*FFFF are not expected in the input
+hex file; they are reserved and always counted as being present in a plane.