Need nroff escape sequence help

[Doug Gwyn <gwyn>]

> I am updating my Diablo 630 filter and would like to implement:
> 
> 	<ESC>5 = reverse half horizontal
> 	<ESC>6 = forward half horizontal

"nroff" uses a table for each supported terminal type that contains
character sequences needed for a variety of functions.  It also
describes the width of each individual character, so at least in
theory it can support proportional printing.  However, its horizontal
spacing is done by a combination of space characters and "plot mode"
escapes.  There is a "narrow space" character but that's it.