
<code>space</code>,
<code>upper</code>, and
<code>xdigit</code>,
each one containing a correspondent pattern.
Each pattern matches any single character that belongs to its class.
</p>

<p>
If called with an argument <code>table</code>,
then it creates those fields inside the given table and
returns that table. 
</p>


<h3><a name="op-len"></a><code>#patt</code></h3>
<p>
Returns a pattern that
matches only if the input string matches <code>patt</code>,
but without consuming any input,
independently of succe