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   groff_out    ( 5 )

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Совместимость (Compatibility)

The intermediate output language of the classical troff was first documented in [CSTR #97] . The groff intermediate output format is compatible with this specification except for the following features.

• The classical quasi device independence is not yet implemented.

• The old hardware was very different from what we use today. So the groff devices are also fundamentally different from the ones in classical troff. For example, the classical PostScript device was called post and had a resolution of 720 units per inch, while groff's ps device has a resolution of 72000 units per inch. Maybe, by implementing some rescaling mechanism similar to the classical quasi device independence, these could be integrated into modern groff.

• The B-spline command D~ is correctly handled by the intermediate output parser, but the drawing routines aren't implemented in some of the postprocessor programs.

• The argument of the commands s and x H has the implicit unit scaled point z in groff, while classical troff had point (p). This isn't an incompatibility, but a compatible extension, for both units coincide for all devices without a sizescale parameter, including all classical and the groff text devices. The few groff devices with a sizescale parameter either did not exist, had a different name, or seem to have had a different resolution. So conflicts with classical devices are very unlikely.

• The position changing after the commands Dp, DP, and Dt is illogical, but as old versions of groff used this feature it is kept for compatibility reasons.

The differences between groff and classical troff are documented in groff_diff(7).