groff: Interpolating Registers
5.6.2 Interpolating Registers
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Numeric registers can be accessed via the '\n' escape.
-- Escape: \ni
-- Escape: \n(id
-- Escape: \n[ident]
Interpolate number register with name IDENT (one-character name I,
two-character name ID). This means that the value of the register
is expanded in-place while 'gtroff' is parsing the input line.
Nested assignments (also called indirect assignments) are possible.
.nr a 5
.nr as \na+\na
\n(as
=> 10
.nr a1 5
.nr ab 6
.ds str b
.ds num 1
\n[a\n[num]]
=> 5
\n[a\*[str]]
=> 6