cording to the following rules:
</p>
<ul>

<li><p>
If the argument is a pattern,
it is returned unmodified.
</p></li>

<li><p>
If the argument is a string,
it is translated to a pattern that matches literally the string.
</p></li>

<li><p>
If the argument is a non-negative number <em>n</em>,
the result is a pattern that matches exactly <em>n</em> characters.
</p></li>

<li><p>
If the argument is a negative number <em>-n</em>,
the result is a pattern that
succeeds only if the input string does not have <em>n