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5.6.4 Assigning Formats

When a register is used, it is always textually replaced (or interpolated) with a representation of that number. This output format can be changed to a variety of formats (numbers, Roman numerals, etc.). This is done using the af request.

— Request: .af ident format

Change the output format of a number register. The first argument ident is the name of the number register to be changed, and the second argument format is the output format. The following output formats are available:

Decimal arabic numbers. This is the default format: 0, 1, 2, 3, ...
Decimal numbers with as many digits as specified. So, ‘00’ would result in printing numbers as 01, 02, 03, ...

In fact, any digit instead of zero does work; gtroff only counts how many digits are specified. As a consequence, af's default format ‘1’ could be specified as ‘0’ also (and exactly this is returned by the \g escape, see below).

Upper-case Roman numerals: 0, I, II, III, IV, ...
Lower-case Roman numerals: 0, i, ii, iii, iv, ...
Upper-case letters: 0, A, B, C, ..., Z, AA, AB, ...
Lower-case letters: 0, a, b, c, ..., z, aa, ab, ...

Omitting the number register format causes a warning of type ‘missing’. See Debugging, for more details. Specifying a nonexistent format causes an error.

The following example produces ‘10, X, j, 010’:

          .nr a 10
          .af a 1           \" the default format
          .af a I
          .af a a
          .af a 001

The largest number representable for the ‘i’ and ‘I’ formats is 39999 (or −39999); UNIX troff uses ‘z’ and ‘w’ to represent 10000 and 5000 in Roman numerals, and so does gtroff. Currently, the correct glyphs of Roman numeral five thousand and Roman numeral ten thousand (Unicode code points U+2182 and U+2181, respectively) are not available.

If ident doesn't exist, it is created.

Changing the output format of a read-only register causes an error. It is necessary to first copy the register's value to a writeable register, then apply the af request to this other register.

— Escape: \gi
— Escape: \g(id
— Escape: \g[ident]

Return the current format of the specified register ident (one-character name i, two-character name id). For example, ‘\ga’ after the previous example would produce the string ‘000’. If the register hasn't been defined yet, nothing is returned.