ss or failure.
(This pattern is called an <em>and predicate</em>
and it is equivalent to
<em>&amp;patt</em> in the original PEG notation.)
</p>


<p>
This pattern never produces any capture.
</p>.


<h3><a name="op-unm"></a><code>-patt</code></h3>
<p>
Returns a pattern that
matches only if the input string does not match <code>patt</code>.
It does not consume any input,
independently of success or failure.
(This pattern is equivalent to
<em>!patt</em> in the original PEG notation.)
</p>

<p>
As an example, 