List of known bugs:

+ The number option doesn't display line numbers in ex append/insert
  mode.

+ The option sidescroll is completely wrong, and setting it does more
  harm than good.

+ When nvi edits files that don't have trailing newlines, it appends
  one, regardless.

+ Open mode is not yet implemented.

+ ^C isn't passed to the shell in the script windows as an interrupt
  character.

+ The options:

	hardtabs, lisp, optimize, redraw, slowopen

  are recognized, but not implemented.  These options are unlikely to
  be implemented, so if you want them you might want to say something!
  I will implement lisp if anyone ever documents how it worked.

+ Screen repainting over slow lines, for some screen changes, isn't
  as good as the historic vi's.

+ The line movement commands ('k', 'j' are easy examples) don't find the
  most attractive cursor position correctly when wrapped lines are longer
  than 80 characters, and they're on the second or subsequent lines.

+ Colon commands longer than a single line cause the display to be
  incorrect.

+ The usages of S_{REDRAW,REFORMAT,REFRESH,RENUMBER,RESIZE} are
  inconsistent, and should be reviewed.  In particular, S_REFRESH
  in any screen redraws all screens.

+ Historic vi permitted :g/xxx/vi, i.e. you could execute ex/vi as
  global commands.  Need to review all of the old commands to verify
  which ones could/could not be used as global commands.

+ If you run out of space in the recovery directory, the recovery
  file is left in place.