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diff --git a/doc/groff.html.node/Identifiers.html b/doc/groff.html.node/Identifiers.html new file mode 100644 index 0000000..5734bb5 --- /dev/null +++ b/doc/groff.html.node/Identifiers.html @@ -0,0 +1,210 @@ +<!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>Identifiers (The GNU Troff Manual)</title> + +<meta name="description" content="Identifiers (The GNU Troff Manual)"> +<meta name="keywords" content="Identifiers (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="Formatter-Instructions.html" rel="next" title="Formatter Instructions"> +<link href="Numeric-Expressions.html" rel="prev" title="Numeric Expressions"> +<style type="text/css"> +<!-- +a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em} +div.example {margin-left: 3.2em} +span.r {font-family: initial; font-weight: normal; font-style: normal} +span:hover a.copiable-link {visibility: visible} +strong.def-name {font-family: monospace; font-weight: bold; font-size: larger} +--> +</style> + + +</head> + +<body lang="en"> +<div class="section-level-extent" id="Identifiers"> +<div class="nav-panel"> +<p> +Next: <a href="Formatter-Instructions.html" accesskey="n" rel="next">Formatter Instructions</a>, Previous: <a href="Numeric-Expressions.html" accesskey="p" rel="prev">Numeric Expressions</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="Identifiers-1">5.5 Identifiers</h3> +<a class="index-entry-id" id="index-identifiers"></a> + +<p>An <em class="dfn">identifier</em> labels a GNU <code class="code">troff</code> datum such as a register, +name (macro, string, or diversion), typeface, color, special character, +character class, environment, or stream. Valid identifiers consist of +one or more ordinary characters. +<a class="index-entry-id" id="index-ordinary-character"></a> +<a class="index-entry-id" id="index-character_002c-ordinary"></a> +An <i class="slanted">ordinary character</i> is an input character that is not the +escape character, a leader, tab, newline, or invalid as GNU <code class="code">troff</code> +input. +</p> +<a class="index-entry-id" id="index-invalid-input-characters"></a> +<a class="index-entry-id" id="index-input-characters_002c-invalid"></a> +<a class="index-entry-id" id="index-characters_002c-invalid-input"></a> +<a class="index-entry-id" id="index-Unicode"></a> +<p>Invalid input characters are a subset of control characters (from the +sets “C0 Controls” and “C1 Controls” as Unicode describes them). +When GNU <code class="code">troff</code> encounters one in an identifier, it produces a +warning in category ‘<samp class="samp">input</samp>’ (see <a class="pxref" href="Warnings.html">Warnings</a>). They are removed +during interpretation: an identifier ‘<samp class="samp">foo</samp>’, followed by an invalid +character and then ‘<samp class="samp">bar</samp>’, is processed as ‘<samp class="samp">foobar</samp>’. +</p> +<p>On a machine using the ISO 646, 8859, or 10646 character encodings, +invalid input characters are <code class="code">0x00</code>, <code class="code">0x08</code>, <code class="code">0x0B</code>, +<code class="code">0x0D</code>–<code class="code">0x1F</code>, and <code class="code">0x80</code>–<code class="code">0x9F</code>. On an +<abbr class="acronym">EBCDIC</abbr> host, they are <code class="code">0x00</code>–<code class="code">0x01</code>, <code class="code">0x08</code>, +<code class="code">0x09</code>, <code class="code">0x0B</code>, <code class="code">0x0D</code>–<code class="code">0x14</code>, +<code class="code">0x17</code>–<code class="code">0x1F</code>, and +<code class="code">0x30</code>–<code class="code">0x3F</code>.<a class="footnote" id="DOCF40" href="groff.html_fot.html#FOOT40"><sup>40</sup></a> Some of these code points are used +by GNU <code class="code">troff</code> internally, making it non-trivial to extend the +program to accept UTF-8 or other encodings that use characters from +these ranges.<a class="footnote" id="DOCF41" href="groff.html_fot.html#FOOT41"><sup>41</sup></a> +</p> +<p>Thus, the identifiers ‘<samp class="samp">br</samp>’, ‘<samp class="samp">PP</samp>’, ‘<samp class="samp">end-list</samp>’, +‘<samp class="samp">ref*normal-print</samp>’, ‘<samp class="samp">|</samp>’, ‘<samp class="samp">@_</samp>’, and ‘<samp class="samp">!"#$%'()*+,-./</samp>’ +are all valid. Discretion should be exercised to prevent confusion. +Identifiers starting with ‘<samp class="samp">(</samp>’ or ‘<samp class="samp">[</samp>’ require care. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.nr x 9 +.nr y 1 +.nr (x 2 +.nr [y 3 +.nr sum1 (\n(x + \n[y]) + error→ a space character is not allowed in an escape + error→ sequence parameter +A:2+3=\n[sum1] +.nr sum2 (\n((x + \n[[y]) +B:2+3=\n[sum2] +.nr sum3 (\n[(x] + \n([y) +C:2+3=\n[sum3] + ⇒ A:2+3=1 B:2+3=5 C:2+3=5 +</pre></div></div> + +<a class="index-entry-id" id="index-_005d_002c-as-part-of-an-identifier"></a> +<p>An identifier with a closing bracket (‘<samp class="samp">]</samp>’) in its name can’t be +accessed with bracket-form escape sequences that expect an identifier as +a parameter. For example, ‘<samp class="samp">\[foo]]</samp>’ accesses the glyph ‘<samp class="samp">foo</samp>’, +followed by ‘<samp class="samp">]</samp>’ in whatever the surrounding context is, whereas +‘<samp class="samp">\C'foo]'</samp>’ formats a glyph named ‘<samp class="samp">foo]</samp>’. Similarly, the +identifier ‘<samp class="samp">(</samp>’ can’t be interpolated <em class="emph">except</em> with bracket +forms. +</p> +<a class="index-entry-id" id="index-refer_002c-and-macro-names-starting-with-_005b-or-_005d"></a> +<a class="index-entry-id" id="index-_005b_002c-macro-names-starting-with_002c-and-refer"></a> +<a class="index-entry-id" id="index-_005d_002c-macro-names-starting-with_002c-and-refer"></a> +<a class="index-entry-id" id="index-macro-names_002c-starting-with-_005b-or-_005d_002c-and-refer"></a> +<p>If you begin a macro, string, or diversion name with either of the +characters ‘<samp class="samp">[</samp>’ or ‘<samp class="samp">]</samp>’, you foreclose use of the <code class="code">grefer</code> +preprocessor, which recognizes ‘<samp class="samp">.[</samp>’ and ‘<samp class="samp">.]</samp>’ as bibliographic +reference delimiters. +</p> +<dl class="first-deffn"> +<dt class="deffn" id="index-_005cA_0027anything_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\A<code class="code">'</code></code><span class="r"><i class="slanted">anything</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cA_0027anything_0027'> ¶</a></span></dt> +<dd><a class="index-entry-id" id="index-_005cA"></a> +<p>Interpolate 1 if <var class="var">anything</var> is a valid identifier, and 0 +otherwise. The delimiter need not be a neutral apostrophe; see +<a class="ref" href="Delimiters.html">Delimiters</a>. Because invalid input characters are removed (see +above), invalid identifiers are empty or contain spaces, tabs, or +newlines. +</p> +<p>You can employ <code class="code">\A</code> to validate a macro argument before using it to +construct another escape sequence or identifier. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.\" usage: .init-coordinate-pair name val1 val2 +.\" Create a coordinate pair where name!x=val1 and +.\" name!y=val2. +.de init-coordinate-pair +. if \A'\\$1' \{\ +. if \B'\\$2' .nr \\$1!x \\$2 +. if \B'\\$3' .nr \\$1!y \\$3 +. \} +.. +.init-coordinate-pair center 5 10 +The center is at (\n[center!x], \n[center!y]). +.init-coordinate-pair "poi→nt" trash garbage \" ignored +.init-coordinate-pair point trash garbage \" ignored + ⇒ The center is at (5, 10). +</pre></div></div> + +<p>In this example, we also validated the numeric arguments; the registers +‘<samp class="samp">point!x</samp>’ and ‘<samp class="samp">point!y</samp>’ remain undefined. See <a class="xref" href="Numeric-Expressions.html">Numeric Expressions</a> for the <code class="code">\B</code> escape sequence. +</p></dd></dl> + +<a class="index-entry-id" id="index-undefined-identifiers"></a> +<a class="index-entry-id" id="index-identifiers_002c-undefined"></a> +<p>How GNU <code class="code">troff</code> handles the interpretation of an undefined +identifier depends on the context. There is no way to invoke an +undefined request; such syntax is interpreted as a macro call instead. +If the identifier is interpreted as a string, macro, or diversion, GNU +<code class="code">troff</code> emits a warning in category ‘<samp class="samp">mac</samp>’, defines it as +empty, and interpolates nothing. If the identifier is interpreted as a +register, GNU <code class="code">troff</code> emits a warning in category ‘<samp class="samp">reg</samp>’, +initializes it to zero, and interpolates that value. See <a class="xref" href="Warnings.html">Warnings</a>, +<a class="ref" href="Interpolating-Registers.html">Interpolating Registers</a>, and <a class="ref" href="Strings.html">Strings</a>. Attempting to use an +undefined typeface, special character, color, character class, +environment, or stream generally provokes an error diagnostic. +</p> +<a class="index-entry-id" id="index-name-space_002c-common_002c-of-macros_002c-diversions_002c-and-strings"></a> +<a class="index-entry-id" id="index-common-name-space-of-macros_002c-diversions_002c-and-strings"></a> +<a class="index-entry-id" id="index-macros_002c-shared-name-space-with-strings-and-diversions"></a> +<a class="index-entry-id" id="index-strings_002c-shared-name-space-with-macros-and-diversions"></a> +<a class="index-entry-id" id="index-diversions_002c-shared-name-space-with-macros-and-strings"></a> +<p>Identifiers for requests, macros, strings, and diversions share one name +space; special characters and character classes another. No other +object types do. +</p> +<div class="example"> +<div class="group"><pre class="example-preformatted">.de xxx +. nop foo +.. +.di xxx +bar +.br +.di +. +.xxx + ⇒ bar +</pre></div></div> + +<p>The foregoing example shows that GNU <code class="code">troff</code> reuses the identifier +‘<samp class="samp">xxx</samp>’, changing it from a macro to a diversion. No warning is +emitted, and the previous contents of ‘<samp class="samp">xxx</samp>’ are lost. +</p> + + +</div> +<hr> +<div class="nav-panel"> +<p> +Next: <a href="Formatter-Instructions.html">Formatter Instructions</a>, Previous: <a href="Numeric-Expressions.html">Numeric Expressions</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> |