Each device control command starts with the letter ‘x’, followed by
a space character (optional or arbitrary space or tab in gtroff)
and a subcommand letter or word; each argument (if any) must be preceded
by a syntactical space. All ‘x’ commands are terminated by a
syntactical line break; no device control command can be followed by
another command on the same line (except a comment).
The subcommand is basically a single letter, but to increase
readability, it can be written as a word, i.e., an arbitrary sequence of
characters terminated by the next tab, space, or newline character. All
characters of the subcommand word but the first are simply ignored. For
example, gtroff outputs the initialization command ‘x i’
as ‘x init’ and the resolution command ‘x r’ as
‘x res’.
In the following, the syntax element ‹line break› means a syntactical line break (see Separation).
xF name‹line break›The ‘F’ stands for Filename.
Use name as the intended name for the current file in error
reports. This is useful for remembering the original file name when
gtroff uses an internal piping mechanism. The input file is not
changed by this command. This command is a gtroff extension.
xf n s‹line break›The ‘f’ stands for font.
Mount font position n (a non-negative integer) with font named s (a text word). See Font Positions.
xH n‹line break›The ‘H’ stands for Height.
Set glyph height to n (a positive integer in scaled points
‘z’). AT&T troff uses the unit points (‘p’)
instead. See Output Language Compatibility.
xi‹line break›The ‘i’ stands for init.
Initialize device. This is the third command of the prologue.
xp‹line break›The ‘p’ stands for pause.
Parsed but ignored. The AT&T troff manual documents
this command as
pause device, can be restarted
but GNU troff output drivers do nothing with this command.
xr n h v‹line break›The ‘r’ stands for resolution.
Resolution is n, while h is the minimal horizontal motion, and v the minimal vertical motion possible with this device; all arguments are positive integers in basic units ‘u’ per inch. This is the second command of the prologue.
xS n‹line break›The ‘S’ stands for Slant.
Set slant to n (an integer in basic units ‘u’).
xs‹line break›The ‘s’ stands for stop.
Terminates the processing of the current file; issued as the last
command of any intermediate troff output.
xt‹line break›The ‘t’ stands for trailer.
Generate trailer information, if any. In GNU troff, this is
ignored.
xT xxx‹line break›The ‘T’ stands for Typesetter.
Set the name of the output driver to xxx, a sequence of
non-whitespace characters terminated by whitespace. The possible names
correspond to those of groff’s -T option. This is the
first command of the prologue.
xu n‹line break›The ‘u’ stands for underline.
Configure underlining of spaces. If n is 1, start
underlining of spaces; if n is 0, stop underlining of spaces.
This is needed for the cu request in nroff mode and is
ignored otherwise. This command is a gtroff extension.
xX anything‹line break›The ‘x’ stands for X-escape.
Send string anything uninterpreted to the device. If the line
following this command starts with a ‘+’ character this line is
interpreted as a continuation line in the following sense. The ‘+’
is ignored, but a newline character is sent instead to the device, the
rest of the line is sent uninterpreted. The same applies to all
following lines until the first character of a line is not a ‘+’
character. This command is generated by the gtroff escape
sequence \X. The line-continuing feature is a gtroff
extension.