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<title>Separation (The GNU Troff Manual)</title>
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<h4 class="subsubsection" id="Separation-1">6.1.1.1 Separation</h4>
<p><abbr class="acronym">AT&T</abbr> <code class="code">troff</code> output has strange requirements regarding
whitespace. The <code class="code">gtroff</code> output parser, however, is more tolerant,
making whitespace maximally optional. Such characters, i.e., the tab,
space, and newline, always have a syntactical meaning. They are never
printable because spacing within the output is always done by
positioning commands.
</p>
<p>Any sequence of space or tab characters is treated as a single
<em class="dfn">syntactical space</em>. It separates commands and arguments, but is
only required when there would occur a clashing between the command code
and the arguments without the space. Most often, this happens when
variable-length command names, arguments, argument lists, or command
clusters meet. Commands and arguments with a known, fixed length need
not be separated by syntactical space.
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<p>A line break is a syntactical element, too. Every command argument can
be followed by whitespace, a comment, or a newline character. Thus a
<em class="dfn">syntactical line break</em> is defined to consist of optional
syntactical space that is optionally followed by a comment, and a
newline character.
</p>
<p>The normal commands, those for positioning and text, consist of a single
letter taking a fixed number of arguments. For historical reasons, the
parser allows stacking of such commands on the same line, but
fortunately, in <code class="code">gtroff</code>’s intermediate output, every command with
at least one argument is followed by a line break, thus providing
excellent readability.
</p>
<p>The other commands—those for drawing and device controlling—have a
more complicated structure; some recognize long command names, and some
take a variable number of arguments. So all ‘<samp class="samp">D</samp>’ and ‘<samp class="samp">x</samp>’
commands were designed to request a syntactical line break after their
last argument. Only one command, ‘<samp class="samp">x X</samp>’<!-- /@w -->, has an argument that
can span several input lines; all other commands must have all of
their arguments on the same line as the command, i.e., the arguments may
not be split by a line break.
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<p>Empty lines (these are lines containing only space and/or a comment),
can occur everywhere. They are just ignored.
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