pan> <span class="identifier">str</span><span class="special">)</span>
<span class="special">{</span>
    <span class="keyword">return</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">(</span><span class="identifier">str</span><span class="special">);</span>
<span class="special">}</span>

<span class="comment">// the following constructs the type of a distinct_spec holding a</span>
<span class="comment">// charset("0-9a-zA