le the expression
        <code class="computeroutput"><span class="identifier">ca</span><span class="special">?</span><span class="identifier">b</span></code> will match any of the following:
      </p>
<pre class="programlisting">cb
cab
</pre>
<p>
        But will not match:
      </p>
<pre class="programlisting">caab
</pre>
<p>
        An atom can also be repeated with a bounded repeat:
      </p>
<p>
        <code class="computeroutput"><span class="identifier">a</span><span class="special">{</span><spa