groff: Copy-in Mode
5.21.1 Copy-in Mode
-------------------
When 'gtroff' reads in the text for a macro, string, or diversion, it
copies the text (including request lines, but excluding escapes) into an
internal buffer. Escapes are converted into an internal form, except
for '\n', '\$', '\*', '\\' and '\<RET>', which are evaluated and
inserted into the text where the escape was located. This is known as
"copy-in" mode or "copy" mode.
What this means is that you can specify when these escapes are to be
evaluated (either at copy-in time or at the time of use) by insulating
the escapes with an extra backslash. Compare this to the '\def' and
'\edef' commands in TeX.
The following example prints the numbers 20 and 10:
.nr x 20
.de y
.nr x 10
\&\nx
\&\\nx
..
.y