s a string <em>xy</em> of length 2,
representing all characters with code
between the codes of <em>x</em> and <em>y</em>
(both inclusive).
</p>

<p>
As an example, the pattern
<code>lpeg.R("09")</code> matches any digit,
and <code>lpeg.R("az", "AZ")</code> matches any ASCII letter.
</p>


<h3><a name="op-s"></a><code>lpeg.S (string)</code></h3>
<p>
Returns a pattern that matches any single character that
appears in the given string.
(The <code>S</code> stands for <em>Set</em>.)
</p>

<p>
As an example, the 