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diff --git a/doc/groff.html.node/Gtroff-Internals.html b/doc/groff.html.node/Gtroff-Internals.html new file mode 100644 index 0000000..2e38fe7 --- /dev/null +++ b/doc/groff.html.node/Gtroff-Internals.html @@ -0,0 +1,187 @@ +<!DOCTYPE html> +<html> +<!-- Created by GNU Texinfo 7.0.3, https://www.gnu.org/software/texinfo/ --> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> +<!-- This manual documents GNU troff version 1.23.0. + +Copyright © 1994-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A +copy of the license is included in the section entitled "GNU Free +Documentation License". --> +<title>Gtroff Internals (The GNU Troff Manual)</title> + +<meta name="description" content="Gtroff Internals (The GNU Troff Manual)"> +<meta name="keywords" content="Gtroff Internals (The GNU Troff Manual)"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta name="viewport" content="width=device-width,initial-scale=1"> + +<link href="index.html" rel="start" title="Top"> +<link href="Request-Index.html" rel="index" title="Request Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="GNU-troff-Reference.html" rel="up" title="GNU troff Reference"> +<link href="Debugging.html" rel="next" title="Debugging"> +<link href="Miscellaneous.html" rel="prev" title="Miscellaneous"> +<style type="text/css"> +<!-- +div.example {margin-left: 3.2em} +--> +</style> + + +</head> + +<body lang="en"> +<div class="section-level-extent" id="Gtroff-Internals"> +<div class="nav-panel"> +<p> +Next: <a href="Debugging.html" accesskey="n" rel="next">Debugging</a>, Previous: <a href="Miscellaneous.html" accesskey="p" rel="prev">Miscellaneous</a>, Up: <a href="GNU-troff-Reference.html" accesskey="u" rel="up">GNU <code class="code">troff</code> Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Request-Index.html" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<h3 class="section" id="gtroff-Internals">5.36 <code class="code">gtroff</code> Internals</h3> + +<a class="index-entry-id" id="index-input-token"></a> +<a class="index-entry-id" id="index-token_002c-input"></a> +<a class="index-entry-id" id="index-output-node"></a> +<a class="index-entry-id" id="index-node_002c-output"></a> +<p><code class="code">gtroff</code> processes input in three steps. One or more input +characters are converted to an <em class="dfn">input token</em>.<a class="footnote" id="DOCF119" href="groff.html_fot.html#FOOT119"><sup>119</sup></a> Then, one or more input tokens are converted to +an <em class="dfn">output node</em>. Finally, output nodes are converted to the +intermediate output language understood by all output devices. +</p> +<p>Actually, before step one happens, <code class="code">gtroff</code> converts certain escape +sequences into reserved input characters (not accessible by the user); +such reserved characters are used for other internal processing also – +this is the very reason why not all characters are valid input. +See <a class="xref" href="Identifiers.html">Identifiers</a>, for more on this topic. +</p> +<p>For example, the input string ‘<samp class="samp">fi\[:u]</samp>’ is converted into a +character token ‘<samp class="samp">f</samp>’, a character token ‘<samp class="samp">i</samp>’, and a special +token ‘<samp class="samp">:u</samp>’ (representing u umlaut). Later on, the character +tokens ‘<samp class="samp">f</samp>’ and ‘<samp class="samp">i</samp>’ are merged to a single output node +representing the ligature glyph ‘<samp class="samp">fi</samp>’ (provided the current font has +a glyph for this ligature); the same happens with ‘<samp class="samp">:u</samp>’. All output +glyph nodes are ‘processed’, which means that they are invariably +associated with a given font, font size, advance width, etc. During the +formatting process, <code class="code">gtroff</code> itself adds various nodes to control +the data flow. +</p> +<p>Macros, diversions, and strings collect elements in two chained lists: a +list of input tokens that have been passed unprocessed, and a list of +output nodes. Consider the following diversion. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.di xxx +a +\!b +c +.br +.di +</pre></div></div> + +<p>It contains these elements. +</p> +<table class="multitable"> +<tbody><tr><td>node list</td><td>token list</td><td>element number</td></tr> +<tr><td><i class="i">line start node</i></td><td>—</td><td>1</td></tr> +<tr><td><i class="i">glyph node <code class="code">a</code></i></td><td>—</td><td>2</td></tr> +<tr><td><i class="i">word space node</i></td><td>—</td><td>3</td></tr> +<tr><td>—</td><td><code class="code">b</code></td><td>4</td></tr> +<tr><td>—</td><td><code class="code">\n</code></td><td>5</td></tr> +<tr><td><i class="i">glyph node <code class="code">c</code></i></td><td>—</td><td>6</td></tr> +<tr><td><i class="i">vertical size node</i></td><td>—</td><td>7</td></tr> +<tr><td><i class="i">vertical size node</i></td><td>—</td><td>8</td></tr> +<tr><td>—</td><td><code class="code">\n</code></td><td>9</td></tr> +</tbody> +</table> + +<a class="index-entry-id" id="index-_005cv_002c-internal-representation"></a> +<p>Elements 1, 7, and 8 are inserted by <code class="code">gtroff</code>; the latter two +(which are always present) specify the vertical extent of the last line, +possibly modified by <code class="code">\x</code>. The <code class="code">br</code> request finishes the +pending output line, inserting a newline input token, which is +subsequently converted to a space when the diversion is reread. Note +that the word space node has a fixed width that isn’t adjustable +anymore. To convert horizontal space nodes back to input tokens, use +the <code class="code">unformat</code> request. +</p> +<p>Macros only contain elements in the token list (and the node list is +empty); diversions and strings can contain elements in both lists. +</p> +<p>The <code class="code">chop</code> request simply reduces the number of elements in a +macro, string, or diversion by one. Exceptions are <em class="dfn">compatibility +save</em> and <em class="dfn">compatibility ignore</em> input tokens, which are ignored. +The <code class="code">substring</code> request also ignores those input tokens. +</p> +<p>Some requests like <code class="code">tr</code> or <code class="code">cflags</code> work on glyph identifiers +only; this means that the associated glyph can be changed without +destroying this association. This can be very helpful for substituting +glyphs. In the following example, we assume that glyph ‘<samp class="samp">foo</samp>’ isn’t +available by default, so we provide a substitution using the +<code class="code">fchar</code> request and map it to input character ‘<samp class="samp">x</samp>’. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.fchar \[foo] foo +.tr x \[foo] +</pre></div></div> + +<p>Now let us assume that we install an additional special font ‘<samp class="samp">bar</samp>’ +that has glyph ‘<samp class="samp">foo</samp>’. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.special bar +.rchar \[foo] +</pre></div></div> + +<p>Since glyphs defined with <code class="code">fchar</code> are searched before glyphs in +special fonts, we must call <code class="code">rchar</code> to remove the definition of the +fallback glyph. Anyway, the translation is still active; ‘<samp class="samp">x</samp>’ now +maps to the real glyph ‘<samp class="samp">foo</samp>’. +</p> +<a class="index-entry-id" id="index-compatibility-mode_002c-and-parameters"></a> +<a class="index-entry-id" id="index-mode_002c-compatibility_002c-and-parameters"></a> +<a class="index-entry-id" id="index-arguments_002c-and-compatibility-mode"></a> +<a class="index-entry-id" id="index-parameters_002c-and-compatibility-mode"></a> +<a class="index-entry-id" id="index-macro-arguments_002c-and-compatibility-mode"></a> +<a class="index-entry-id" id="index-request-arguments_002c-and-compatibility-mode"></a> +<p>Macro and request arguments preserve compatibility mode enablement. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.cp 1 \" switch to compatibility mode +.de xx +\\$1 +.. +.cp 0 \" switch compatibility mode off +.xx caf\['e] + ⇒ café +</pre></div></div> + +<p>Since compatibility mode is enabled while <code class="code">de</code> is invoked, the +macro <code class="code">xx</code> enables compatibility mode when it is called. Argument +<code class="code">$1</code> can still be handled properly because it inherits the +compatibility mode enablement status that was active at the point where +<code class="code">xx</code> was called. +</p> +<p>After interpolation of the parameters, the compatibility save and +restore tokens are removed. +</p> + + + +</div> +<hr> +<div class="nav-panel"> +<p> +Next: <a href="Debugging.html">Debugging</a>, Previous: <a href="Miscellaneous.html">Miscellaneous</a>, Up: <a href="GNU-troff-Reference.html">GNU <code class="code">troff</code> Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Request-Index.html" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |