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<title>Differences from AT&T ms (The GNU Troff Manual)</title>
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<h4 class="subsection" id="Differences-from-AT_0026T-ms-1">4.6.7 Differences from <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp></h4>
<a class="index-entry-id" id="index-ms-macros_002c-groff-differences-from-AT_0026T"></a>
<a class="index-entry-id" id="index-AT_0026T-ms_002c-macro-package-differences"></a>
<p>The <code class="code">groff</code> <samp class="file">ms</samp> macros are an independent reimplementation,
using no <abbr class="acronym">AT&T</abbr> code. Since they take advantage of the extended
features of <code class="code">groff</code>, they cannot be used with <abbr class="acronym">AT&T</abbr>
<code class="code">troff</code>. <code class="code">groff</code> <samp class="file">ms</samp> supports features described above
as Berkeley and Tenth Edition Research Unix extensions, and adds several
of its own.
</p>
<ul class="itemize mark-bullet">
<li>The internals of <code class="code">groff</code> <samp class="file">ms</samp> differ from the internals of
<abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp>. Documents that depend upon implementation
details of <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> may not format properly with
<code class="code">groff</code> <samp class="file">ms</samp>. Such details include macros whose function was
not documented in the <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp>
manual.<a class="footnote" id="DOCF14" href="groff.html_fot.html#FOOT14"><sup>14</sup></a>
</li><li>The error-handling policy of <code class="code">groff</code> <samp class="file">ms</samp> is to detect and
report errors, rather than to ignore them silently.
</li><li>Tenth Edition Research Unix supported <code class="code">P1</code>/<code class="code">P2</code> macros to bracket code
examples; <code class="code">groff</code> <samp class="file">ms</samp> does not.
</li><li><code class="code">groff</code> <samp class="file">ms</samp> does not work in GNU <code class="code">troff</code>’s
<abbr class="acronym">AT&T</abbr> compatibility mode. If loaded when that mode is enabled,
it aborts processing with a diagnostic message.
</li><li>Multiple line spacing is not supported. Use a larger vertical spacing
instead.
</li><li><code class="code">groff</code> <samp class="file">ms</samp> uses the same header and footer defaults in both
<code class="code">nroff</code> and <code class="code">troff</code> modes as <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> does in
<code class="code">troff</code> mode; <abbr class="acronym">AT&T</abbr>’s default in <code class="code">nroff</code> mode is to
put the date, in U.S. traditional format (e.g., “January 1, 2021”),
in the center footer (the <code class="code">CF</code> string).
</li><li>Many <code class="code">groff</code> <samp class="file">ms</samp> macros, including those for paragraphs,
headings, and displays, cause a reset of paragraph rendering parameters,
and may change the indentation; they do so not by incrementing or
decrementing it, but by setting it absolutely. This can cause problems
for documents that define additional macros of their own that try to
manipulate indentation. Use the <samp class="file">ms</samp> <code class="code">RS</code> and <code class="code">RE</code>
macros instead of the <code class="code">in</code> request.
</li><li><a class="index-entry-id" id="index-fractional-type-sizes-in-ms-macros"></a>
<a class="index-entry-id" id="index-ms-macros_002c-fractional-type-sizes-in"></a>
<abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> interpreted the values of the registers
<code class="code">PS</code> and <code class="code">VS</code> in points, and did not support the use of
scaling units with them. <code class="code">groff</code> <samp class="file">ms</samp> interprets values of
the registers <code class="code">PS</code>, <code class="code">VS</code>, <code class="code">FPS</code>, and <code class="code">FVS</code> equal to
or larger than 1,000 (one thousand) as decimal fractions multiplied
by 1,000.<a class="footnote" id="DOCF15" href="groff.html_fot.html#FOOT15"><sup>15</sup></a> This threshold makes use of a
scaling unit with these parameters practical for high-resolution
devices while preserving backward compatibility. It also permits
expression of non-integral type sizes. For example, ‘<samp class="samp">groff
-rPS=10.5p</samp>’ at the shell prompt is equivalent to placing ‘<samp class="samp">.nr PS
10.5p</samp>’ at the beginning of the document.
</li><li><abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp>’s <code class="code">AU</code> macro supported arguments used with
some document types; <code class="code">groff</code> <samp class="file">ms</samp> does not.
</li><li>Right-aligned displays are available. The <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp>
manual observes that “it is tempting to assume that ‘<samp class="samp">.DS R</samp>’ will
right adjust lines, but it doesn’t work”. In <code class="code">groff</code> <samp class="file">ms</samp>,
it does.
</li><li>To make <code class="code">groff</code> <samp class="file">ms</samp> use the default page offset (which also
specifies the left margin), the <code class="code">PO</code> register must stay undefined
until the first <samp class="file">ms</samp> macro is called.
<p>This implies that ‘<samp class="samp">\n[PO]</samp>’ should not be used early in the
document, unless it is changed also: accessing an undefined register
automatically defines it.
</p>
</li><li><code class="code">groff</code> <samp class="file">ms</samp> supports the <code class="code">PN</code> register, but it is not
necessary; you can access the page number via the usual <code class="code">%</code>
register and invoke the <code class="code">af</code> request to assign a different format
to it if desired.<a class="footnote" id="DOCF16" href="groff.html_fot.html#FOOT16"><sup>16</sup></a>
</li><li>The <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> manual documents registers <code class="code">CW</code> and
<code class="code">GW</code> as setting the default column width and “intercolumn gap”,
respectively, and which applied when <code class="code">MC</code> was called with fewer
than two arguments. <code class="code">groff</code> <samp class="file">ms</samp> instead treats <code class="code">MC</code>
without arguments as synonymous with <code class="code">2C</code>; there is thus no
occasion for a default column width register. Further, the <code class="code">MINGW</code>
register and the second argument to <code class="code">MC</code> specify a <em class="emph">minimum</em>
space between columns, not the fixed gutter width of <abbr class="acronym">AT&T</abbr>
<samp class="file">ms</samp>.
</li><li>The <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> manual did not document the <code class="code">QI</code>
register; Berkeley and <code class="code">groff</code> <samp class="file">ms</samp> do.
</li></ul>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cn_005bGS_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[GS]</code></strong><a class="copiable-link" href='#index-_005cn_005bGS_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-GS-_005bms_005d"></a>
<p>The register <code class="code">GS</code> is set to 1 by the <code class="code">groff</code> <samp class="file">ms</samp>
macros, but is not used by the <abbr class="acronym">AT&T</abbr> <samp class="file">ms</samp> package.
Documents that need to determine whether they are being formatted with
<code class="code">groff</code> <samp class="file">ms</samp> or another implementation should test this
register.
</p></dd></dl>
<ul class="mini-toc">
<li><a href="Missing-Unix-Version-7-ms-Macros.html" accesskey="1">Unix Version 7 <samp class="file">ms</samp> macros not implemented by <code class="code">groff</code> <samp class="file">ms</samp></a></li>
</ul>
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