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6.1 'gtroff' Output
===================

This section describes the 'groff' intermediate output format produced
by GNU 'troff'.

   As 'groff' is a wrapper program around GNU 'troff' and automatically
calls an output driver (or "postprocessor"), this output does not show
up normally.  This is why it is called _intermediate_.  'groff' provides
the option '-Z' to inhibit postprocessing such that the produced
intermediate output is sent to standard output just as it is when
calling GNU 'troff' directly.

   Here, the term "troff output" describes what is output by GNU
'troff', while "intermediate output" refers to the language that is
accepted by the parser that prepares this output for the output drivers.
This parser handles whitespace more flexibly than AT&T's implementation
and implements obsolete elements for compatibility; otherwise, both
formats are the same.(1)  (*note gtroff Output-Footnote-1::)

   The main purpose of the intermediate output concept is to facilitate
the development of postprocessors by providing a common programming
interface for all devices.  It has a language of its own that is
completely different from the 'gtroff' language.  While the 'gtroff'
language is a high-level programming language for text processing, the
intermediate output language is a kind of low-level assembler language
by specifying all positions on the page for writing and drawing.

   The intermediate output produced by 'gtroff' is fairly readable,
while output from AT&T 'troff' is rather hard to understand because of
strange habits that are still supported, but not used any longer by
'gtroff'.

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