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<h2 class="section" id="sec100">B.1  Commands and Environments</h2>
<ul>
<li><a href="manual023.html#sec101">Command Names and Arguments</a>
</li><li><a href="manual023.html#sec102">Environments</a>
</li><li><a href="manual023.html#sec103">Fragile Commands</a>
</li><li><a href="manual023.html#sec104">Declarations</a>
</li><li><a href="manual023.html#sec105">Invisible Commands</a>
</li><li><a href="manual023.html#sec106">The <span class="c013">\\</span> Command</a>
</li></ul>
<h3 class="subsection" id="sec101">B.1.1  Command Names and Arguments</h3>
<p>L<sup>A</sup>T<sub>E</sub>X comments that start with “<code>%</code>” and end at end of line are ignored and produce no output.
Usually, H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A ignore such comments. However, H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A processes
text that follows “<code>%HEVEA</code>” and some other comments have a specific meaning to it (see
section <a href="manual007.html#comments">5.3</a>).</p><p><a id="hevea_default143"></a>
Command names follow strict L<sup>A</sup>T<sub>E</sub>X syntax. That is, apart from
<code>#</code>, <code>$</code>, <code>~</code>, <code>_</code> and <code>^</code>, they either are
“<code>\</code>” followed by a single non-letter character or
“<code>\</code>” followed by a sequence of letters.
Additionally, the letter sequence may be preceded by “<code>@</code>”
(and this is the case of many of H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A internal commands), or
terminated by “<code>*</code>” (starred variants are implemented as plain
commands).</p><p>Users are strongly advised to follow strict L<sup>A</sup>T<sub>E</sub>X syntax for
arguments. That is, mandatory arguments are enclosed in curly braces
<code>{</code>… <code>}</code> and braces inside arguments must be properly
balanced.
Optional arguments are enclosed in square brackets <code>[</code>…
<code>]</code>.
However, H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A does its best to read arguments even when they are
not enclosed in curly braces.
Such arguments are a single, different from “<code>\</code>”, “<code>{</code>”
and “<code> </code>”, character or
a command name.
Thus, constructs such as <code>\'ecole</code>,
<code>$a_1$</code> or <code>$a_\Gamma$</code> are
recognized and processed as école <span class="c019">a</span><sub>1</sub> and <span class="c019">a</span><sub>Γ</sub>.
By contrast, <code>a^\mbox{...}</code> is not recognized
and must be written <code>a^{\mbox{...}}</code>.</p><p>Also note that, by contrast with L<sup>A</sup>T<sub>E</sub>X, comments are parsed during
argument scanning, as an important consequence brace nesting is also
checked inside comments.</p><p><a id="hevea_default144"></a>
<a id="hevea_default145"></a>
With respect to previous versions,
H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A has been improved as regards emulation of complicated
argument passing. That is,
commands and their arguments can now appear in
different static text bodies. As a consequence,
H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A correctly processes the following source:
</p><pre class="verbatim">\newcommand{\boite}{\textbf}
\boite{In bold}
</pre><p>
The definition of <code>\boite</code> makes it reduces as
<code>\textbf</code> and H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A succeeds in fetching the argument
“<code>{In bold}</code>”. We get
</p><blockquote class="quote">
<span class="c023">In bold</span>
</blockquote><p>The above example arguably is no “legal” L<sup>A</sup>T<sub>E</sub>X,
but H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A handles it.
Of course, there remains
numerous “clever” L<sup>A</sup>T<sub>E</sub>X tricks that exploits T<sub>E</sub>X internal
behaviour, which H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A does not handle.
For instance consider the following source:
</p><pre class="verbatim">\newcommand{\boite}[1]{\textbf#1}
\boite{{In bold}, Not in Bold.}
</pre><p>
L<sup>A</sup>T<sub>E</sub>X typesets the text “In bold” using bold font, leaving
the rest of the text alone. While H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A typesets everything using
bold font. Here is H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A output:
</p><blockquote class="quote">
<span class="c023">In bold, Not in Bold.</span>
</blockquote><p>
Note that, in most similar situations, H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A will likely crash.</p><p>As a conclusion of this important section,
Users are strongly advised to use ordinary command names and
curly braces and not to think too much the T<sub>E</sub>X way.</p>
<h3 class="subsection" id="sec102">B.1.2  Environments</h3>
<p>Environment opening and closing is performed like in L<sup>A</sup>T<sub>E</sub>X, with
<code>\begin{</code><span class="c019">env</span><code>}</code> and
<code>\end{</code><span class="c019">env</span><code>}</code>.
The <code>*</code>-form of an environment is a plain environment.</p><p>It is not advised to use <code>\</code><span class="c019">env</span> and
<code>\end</code><span class="c019">env</span> in place of <code>\begin{</code><span class="c019">env</span><code>}</code> and
<code>\end{</code><span class="c019">env</span><code>}</code>.</p>
<h3 class="subsection" id="sec103">B.1.3  Fragile Commands</h3>
<p>
Fragile commands are not relevant to H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A and <code>\protect</code> is
defined as a null command.</p>
<h3 class="subsection" id="sec104">B.1.4  Declarations</h3>
<p>
Scope rules are the same as in L<sup>A</sup>T<sub>E</sub>X.</p>
<h3 class="subsection" id="sec105">B.1.5  Invisible Commands</h3>
<p>
I am a bit lost here. However spaces in the output should correspond
to users expectations. Note that, to H<span class="c016"><sup>E</sup></span>V<span class="c016"><sup>E</sup></span>A being
invisible commands is a static property attached to command name.</p>
<h3 class="subsection" id="sec106">B.1.6  The <span class="c013">\\</span> Command</h3>
<p>The <code>\\</code> and <code>\\*</code> commands are the same, they perform a
line break, except inside arrays where they end the current row.
Optional arguments to <code>\\</code> and <code>\\*</code> are ignored.</p>
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