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-<head>
-<title>UK TeX FAQ -- question label cvtlatex</title>
-</head><body>
-<h3>Transcribing LaTeX command definitions</h3>
-<p/>At several places in this FAQ, questions are answered in terms
-of how to program a LaTeX macro. Sometimes, these macros might
-also help users of Plain TeX or other packages; this answer
-attempts to provide a rough-and-ready guide to transcribing such macro
-definitions for use in other packages.
-<p/>The reason LaTeX has commands that replace <code>\</code><code>def</code>, is that
-there&#8217;s a general philosophy within LaTeX that the user should be
-protected from himself: the user has different commands according to
-whether the command to be defined exists (<code>\</code><code>renewcommand</code>) or not
-(<code>\</code><code>newcommand</code>), and if its status proves not as the user expected,
-an error is reported. A third definition command,
-<code>\</code><code>providecommand</code>, only defines if the target is not already
-defined; LaTeX has no direct equivalent of <code>\</code><code>def</code>, which ignores
-the present state of the command. The final command of this sort is
-<code>\</code><code>DeclareRobustCommand</code>, which creates a command which is &#8220;robust&#8221;
-(i.e., will not expand if subjected to LaTeX &#8220;protected
-expansion&#8221;); from the Plain TeX user&#8217;s point of view,
-<code>\</code><code>DeclareRobustCommand</code> should be treated as a non-checking version
-of <code>\</code><code>newcommand</code>.
-<p/>LaTeX commands are, by default, defined <code>\</code><code>long</code>; an optional <code>*</code>
-between the <code>\</code><code>newcommand</code> and its (other) arguments specifies that
-the command is <em>not</em> to be defined <code>\</code><code>long</code>. The <code>*</code> is
-detected by a command <code>\</code><code>@ifstar</code> which uses <code>\</code><code>futurelet</code> to switch
-between two branches, and gobbles the <code>*</code>: LaTeX users are
-encouraged to think of the <code>*</code> as part of the command name.
-<p/>LaTeX&#8217;s checks for unknown command are done by <code>\</code><code>ifx</code> comparison
-of a <code>\</code><code>csname</code> construction with <code>\</code><code>relax</code>; since the command name
-argument is the desired control sequence name, this proves a little
-long-winded. Since <code>#1</code> is the requisite argument, we have:
-<blockquote>
-
-<pre>
-\expandafter\ifx
- \csname\expandafter\@gobble\string#1\endcsname
- \relax
- ...
-</pre>
-</blockquote><p>
-(<code>\</code><code>@gobble</code> simply throws away its argument).
-<p/>The arguments of a LaTeX command are specified by two optional
-arguments to the defining command: a count of arguments (0&#8211;9: if the
-count is 0, the optional count argument may be omitted), and a default
-value for the first argument, if the defined command&#8217;s first argument
-is to be optional. So:
-<blockquote>
-<pre>
-\newcommand\foo{...}
-\newcommand\foo[0]{...}
-\newcommand\foo[1]{...#1...}
-\newcommand\foo[2][boo]{...#1...#2...}
-</pre>
-</blockquote><p>
-In the last case, <code>\</code><code>foo</code> may be called as <code>\</code><code>foo{goodbye}</code>,
-which is equivalent to <code>\</code><code>foo[boo]{goodbye}</code> (employing the
-default value given for the first argument), or as
-<code>\</code><code>foo[hello]{goodbye}</code> (with an explicit first argument).
-<p/>Coding of commands with optional arguments is exemplified by the
-coding of the last <code>\</code><code>foo</code> above:
-<blockquote>
-<pre>
-\def\foo{\futurelet\next\@r@foo}
-\def\@r@foo{\ifx\next[%
- \let\next\@x@foo
- \else
- \def\next{\@x@foo[boo]}%
- \fi
- \next
-}
-\def\@x@foo[#1]#2{...#1...#2...}
-</pre>
-</blockquote><p>
-<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=cvtlatex">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=cvtlatex</a>
-</body>