🚀 go-pugleaf

Sorry Andries.

In article <rr|*i34@sea.sm.unisys.com> eggert@sm.unisys.com (Paul Eggert) writes:
! This may arise from a common problem: in some buggy ditroffs, \fP
! doesn't work if you're switching among fonts not mounted by default.
! A workaround is to place a directive like
! 
! 	.fp 4 C
! 
! at the start of the input, substituting some unused font number for `4'.
! This will permanently mount font C, dodging the bug.
! 
Ahhh this explains something else I saw yesterday. 
Until now I was using an explicit .ft CW inside my .(l .(b .(z
to make sure that the output in keeps (-me style) was in CW font.
I noticed I also had a .nr df 7 which is supposed to set the font
inside keeps to font number 7 == CW for me. I then wondered, why do I then
also *explicitly* say .fT CW (you see you do these things and forget why you
did them). I chased it all the way to the .@F macro in tmac.e. 
This macro is used to control the font inside keeps.
Here is the macro.
.de @F
.nr ~ \\$1
.if \\n~>0 \
\{\
.	ul 0
.	if \\n~>4 \			*****************************
.		nr ~ \\n($b
.	ft \\n~
.\}
.rr ~
..
This code explicitly stop you from using any fonts mounted after 4.
I wondered why. Indeed, I replaced the macro without the test.
However, in light of what Paul just said, this magical feature might
just be neceesary for "buggy" ditroffs (is there any other type?).