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<title>The Implicit Page Trap (The GNU Troff Manual)</title>
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<h4 class="subsubsection" id="The-Implicit-Page-Trap-1">5.28.1.2 The Implicit Page Trap</h4>
<a class="index-entry-id" id="index-implicit-trap"></a>
<a class="index-entry-id" id="index-trap_002c-implicit"></a>
<a class="index-entry-id" id="index-page-break-2"></a>
<a class="index-entry-id" id="index-break_002c-page-2"></a>
<a class="index-entry-id" id="index-page-ejection-2"></a>
<a class="index-entry-id" id="index-ejection_002c-page-2"></a>
<p>If, after starting GNU <code class="code">troff</code> without loading a macro package, you
use the <code class="code">ptr</code> request to dump a list of the active traps to the
standard error stream,<a class="footnote" id="DOCF109" href="groff.html_fot.html#FOOT109"><sup>109</sup></a> nothing is reported.
Yet the <code class="code">.t</code> register will report a steadily decreasing value with
every output line your document produces, and once the value of
<code class="code">.t</code> gets to within <code class="code">.V</code> of zero, you will notice that
something trap-like happens—the page is ejected, a new one begins, and
the value of <code class="code">.t</code> becomes large once more.
</p>
<p>This <em class="dfn">implicit page trap</em> always exists in the top-level
diversion;<a class="footnote" id="DOCF110" href="groff.html_fot.html#FOOT110"><sup>110</sup></a> it works like a trap in some
ways but not others. Its purpose is to eject the current page and start
the next one. It has no name, so it cannot be moved or deleted with
<code class="code">wh</code> or <code class="code">ch</code> requests. You cannot hide it by placing another
trap at its location, and can move it only by redefining the page length
with <code class="code">pl</code>. Its operation is suppressed when vertical page traps
are disabled with GNU <code class="code">troff</code>’s <code class="code">vpt</code> request.
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