6.2.2.5 Legacy Compressed Encoding

AT&T troff output primarily emitted glyphs by writing two digits (a motion) followed by a single character corresponding to a glyph. This syntax is less a command itself than a compressed encoding of the c and h commands.

ddg

Move right dd (exactly two decimal digits) basic units ‘u’, then print glyph g (represented as a single character).

In GNU troff, arbitrary syntactical space around and within this command is allowed. Only when a preceding command on the same line ends with an argument of variable length is a separating space obligatory. In AT&T troff, large clusters of these and other commands are used, mostly without spaces; this made such output almost unreadable.

For modern high-resolution devices, this command is impractical because the widths of the glyphs have a greater magnitude in basic units than two decimal digits can represent. In GNU troff, this optimization is used only for the devices X75, X75-12, X100, and X100-12. For other devices, the commands ‘t’ and ‘u’ produce more readable output.