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<h3 class="section" id="Manipulating-Spacing-1">5.11 Manipulating Spacing</h3>
<a class="index-entry-id" id="index-manipulating-spacing"></a>
<a class="index-entry-id" id="index-spacing_002c-manipulating"></a>
<p>A break causes the formatter to update the vertical drawing position at
which the new text baseline is aligned. You can alter this location.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002esp"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.sp</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">distance</i></span>]</var><a class="copiable-link" href='#index-_002esp'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-sp"></a>
<p>Break and move the next text baseline down by <var class="var">distance</var>, or until
springing a page location trap.<a class="footnote" id="DOCF62" href="groff.html_fot.html#FOOT62"><sup>62</sup></a>
If invoked with the no-break control character, <code class="code">sp</code> moves the
pending output line’s text baseline by <var class="var">distance</var>. A negative
<var class="var">distance</var> will not reduce the position of the text baseline below
zero. Inside a diversion, any <var class="var">distance</var> argument is ignored. The
default scaling unit is ‘<samp class="samp">v</samp>’. If <var class="var">distance</var> is not specified,
‘<samp class="samp">1v</samp>’ is assumed.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.pl 5v \" Set page length to 5 vees.
.de xx
\-\-\-
. br
..
.wh 0 xx \" Set a trap at the top of the page.
foo on page \n%
.sp 2v
bar on page \n%
.sp 50v \" This will cause a page break.
baz on page \n%
.pl \n(nlu \" Truncate page to current position.
⇒ ---
⇒ foo on page 1
⇒
⇒
⇒ bar on page 1
⇒ ---
⇒ baz on page 2
</pre></div></div>
<p>You might use the following macros to set the baseline of the next
output text at a given distance from the top or the bottom of the page.
We subtract one line height (<code class="code">\n[.v]</code>) because the <code class="code">|</code>
operator moves to one vee below the page top (recall <a class="ref" href="Numeric-Expressions.html">Numeric Expressions</a>).
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de y-from-top-down
. sp |\\$1-\\n[.v]u
..
.
.de y-from-bot-up
. sp |\\n[.p]u-\\$1-\\n[.v]u
..
</pre></div></div>
<p>A call to ‘<samp class="samp">.y-from-bot-up 10c</samp>’ means that the next text baseline
will be 10 cm from the bottom edge of the paper.
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_002els"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.ls</code></strong> <var class="def-var-arguments">[<span class="r"><i class="slanted">count</i></span>]</var><a class="copiable-link" href='#index-_002els'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-ls"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_005b_002eL_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.L]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002eL_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002eL"></a>
<a class="index-entry-id" id="index-double_002dspacing-_0028ls_0029"></a>
<p>Set the line spacing; add <var class="var">count</var>−1<!-- /@w --> blank lines after each
line of text. With no argument, GNU <code class="code">troff</code> uses the previous
value before the last <code class="code">ls</code> call. The default is <code class="code">1</code>.
</p>
<a class="index-entry-id" id="index-line-spacing-register-_0028_002eL_0029"></a>
<p>The read-only register <code class="code">.L</code> contains the current line spacing; it
is associated with the environment (see <a class="pxref" href="Environments.html">Environments</a>).
</p></dd></dl>
<p>The <code class="code">ls</code> request is a coarse mechanism. See <a class="xref" href="Changing-the-Type-Size.html">Changing the Type Size</a>, for the requests <code class="code">vs</code> and <code class="code">pvs</code> as alternatives to
<code class="code">ls</code>.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cx_0027spacing_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\x<code class="code">'</code></code><span class="r"><i class="slanted">spacing</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cx_0027spacing_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cx"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_005b_002ea_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.a]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002ea_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002ea"></a>
<p>Sometimes, an output line requires additional vertical spacing, for
instance to allow room for a tall construct like an inline equation with
exponents or subscripts (particularly if they are iterated). The
<code class="code">\x</code> escape sequence takes a delimited measurement (like
‘<samp class="samp">\x'3p'</samp>’) to increase the vertical spacing of the pending output
line. The default scaling unit is ‘<samp class="samp">v</samp>’. If the measurement is
positive, extra vertical space is inserted below the current line; a
negative measurement adds space above. If <code class="code">\x</code> is applied to the
pending output line multiple times, the maxima of the positive and
negative adjustments are separately applied. The delimiter need not be
a neutral apostrophe; see <a class="ref" href="Delimiters.html">Delimiters</a>.
</p>
<a class="index-entry-id" id="index-extra-post_002dvertical-line-space-register-_0028_002ea_0029"></a>
<p>The <code class="code">.a</code> read-only register contains the extra vertical spacing
<em class="emph">after</em> the text baseline of the most recently emitted output line.
(In other words, it is the largest positive argument to <code class="code">\x</code>
encountered on that line.) This quantity is exposed via a register
because if an output line requires this “extra post-vertical line
spacing”, and the subsequent output line requires “extra pre-vertical
line spacing” (a negative argument to <code class="code">\x</code>), then applying both
can lead to excessive spacing between the output lines. Text that is
piling high on line <var class="var">n</var> might not require (as much) extra
pre-vertical line spacing if line <var class="var">n</var>−1 carries extra
post-vertical line spacing.
</p>
<p>Use of <code class="code">\x</code> can be necessary in combination with the
bracket-building escape sequence <code class="code">\b</code>,<a class="footnote" id="DOCF63" href="groff.html_fot.html#FOOT63"><sup>63</sup></a> as the following example shows.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.nf
This is a test of \[rs]b (1).
This is a test of \[rs]b (2).
This is a test of \b'xyz'\x'-1m'\x'1m' (3).
This is a test of \[rs]b (4).
This is a test of \[rs]b (5).
⇒ This is a test of \b (1).
⇒ This is a test of \b (2).
⇒ x
⇒ This is a test of y (3).
⇒ z
⇒ This is a test of \b (4).
⇒ This is a test of \b (5).
</pre></div></div>
</dd></dl>
<p>Without <code class="code">\x</code>, the backslashes on the lines marked ‘<samp class="samp">(2)</samp>’ and
‘<samp class="samp">(4)</samp>’ would be overprinted.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002ens"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.ns</code></strong><a class="copiable-link" href='#index-_002ens'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-ns"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_002ers"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.rs</code></strong><a class="copiable-link" href='#index-_002ers'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-rs"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_005b_002ens_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.ns]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002ens_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002ens-1"></a>
<a class="index-entry-id" id="index-sp-request_002c-and-no_002dspace-mode"></a>
<a class="index-entry-id" id="index-no_002dspace-mode-_0028ns_0029"></a>
<a class="index-entry-id" id="index-mode_002c-no_002dspace-_0028ns_0029"></a>
<a class="index-entry-id" id="index-blank-lines_002c-disabling"></a>
<a class="index-entry-id" id="index-lines_002c-blank_002c-disabling"></a>
<p>Enable <em class="dfn">no-space mode</em>. Vertical spacing, whether by <code class="code">sp</code>
requests or blank input lines, is disabled. The <code class="code">bp</code> request to
advance to the next page is also disabled, unless it is accompanied by a
page number (see <a class="pxref" href="Page-Control.html">Page Control</a>). No-space mode ends automatically
when text<a class="footnote" id="DOCF64" href="groff.html_fot.html#FOOT64"><sup>64</sup></a> is formatted for output <a class="footnote" id="DOCF65" href="groff.html_fot.html#FOOT65"><sup>65</sup></a> or the <code class="code">rs</code> request is invoked, which ends
no-space mode. The read-only register <code class="code">.ns</code> interpolates a Boolean
value indicating the enablement of no-space mode.
</p>
<p>A paragraphing macro might ordinarily insert vertical space to separate
paragraphs. A section heading macro could invoke <code class="code">ns</code> to suppress
this spacing for the first paragraph in a section.
</p></dd></dl>
</div>
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