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In article <14365@watdragon.waterloo.edu> tbray@watsol.waterloo.edu (Tim Bray) writes:
>Apologies for cluttering net-bandwidth; couldn't get mail through.
>
>A tiny weeny nit, but:  In various troffs, including ditroff, you can't 
>.ss
>or even
>'ss
>in the middle of an output line and have it take effect right there.  (Bet
>a substantial proportion of (even moderately serious) troff hacks don't
>know what .ss does).
Without looking at the manual (since I left it a home :-):
	.ss == set space character size where the value is entered is
something like N/36 ems (or is it ens?).

>This behaviour is not documented as far as I know, so it should be
>documented or fixed.

The reason is simple why this does not work.  It is were this is interpreted.
Like the .bd, the .ss is interpreted on output.  I do not know the reasoning,
but (as I try to remember since it has been 4 years since I hacked at troff)
this number is not stored in the "magic cookie" of each character and needs
to be in effect when troff tries to properly adjust the margins.  It is also
the same for emboldening since the widths of the characters change and it
needs to know this information on output.  The short of it is because it is
interpreted on output and not input.

Oh, and in a backward sort of way, it is... unfortunatly it assumes that
the  reader knows about troff internals.  It is tied in with the same
reasons that .bd and .cs (do *you* know what that one is) have to be in
effect when you reread a diversion... because they are interpreted on
output, not input.  See the info on diversions (like I said, my manual
is not handy).

NOTE
I have mentioned it once before and before I get alot of mail asking what
the "magic cookie" is: it is what the internal representation of a character
is in troff (I do not remember if it is the same in C/A/T troff since it has
been even longer since I pulled the lid off of that beastie).  In ditroff,
it is a 32-bit quantity that contains size, character, font, motion, etc.
informtion that is also context based (i.e. a charcter does not have spacing
info, but does have width info (16-bits)).  Any attempts at reimplementation
should concentrate on making this "magic cookie" more flexible--or at least
give us more than 16-bits to figure movement.

-- 
scott barman
{gatech, emory}!dtscp1!scott