es <code>patt</code> <code>n</code> characters behind
      the current position, consuming no input</td></tr>
</tbody></table>

<p>As a very simple example,
<code>lpeg.R("09")^1</code> creates a pattern that
matches a non-empty sequence of digits.
As a not so simple example,
<code>-lpeg.P(1)</code>
(which can be written as <code>lpeg.P(-1)</code>
or simply <code>-1</code> for operations expecting a pattern)
matches an empty string only if it cannot match a single character;
so, it succeeds only at the subj