#once #create message
.ND
.tr %$
.EQ
delim $$
.EN
.LP
Of course the thing with bars or braces around it can
still be part of larger expressions: the input
   .EQ
   left | {a over b ~+~ c over d} over 2 right | over a+b+c+d
   .EN
produces
.EQ
left | {a over b ~+~ c over d} over 2 right | over a+b+c+d
.EN

For practice, modify file "Example" so it produces output
that looks like this, then type "ready".
.pl 1
#once #create Ref
.LP
.EQ
left |
{a over b ~+~ c over d} over 2
right |
sup half
.EN
.pl 1
#once #create Example
.LP
.EQ
replace me
.EN
.pl 1
#
#once neqn Ref | nroff >X1 &
#once neqn message Ref | nroff -T$term %s/tinyms -
#user
neqn Example | nroff >X2
#cmp X1 X2
#log
#next
12.1d 10