ntersection and set subtraction operators (+ and binary -)
<li>Low-precedence union operator (|)
</ol>

<p><b>Note:</b> Because the operator characters have special meaning,
you should avoid creating a category that uses any of them in it's name.
For example, the category "db-tests" could not be used on the command
line, since it appears to means "run category db, except for category tests."
The same limitation applies to characters that have special meaning for
the shell you are using.

<p>For a clear unde