"last_modified", and they are customizable.
	</dd>
	<dt>AND</dt>
	<dd>
		AND operator is the default conjunction operator. You can omit it from
		a query. AND operator matches documents where both terms exist
		anywhere in the text of a single document.
		<pre>Fess AND CodeLibs</pre>
	</dd>
	</dd>
	<dt>OR</dt>
	<dd>
		OR operator matches documents where any terms exist anywhere in the
		text of a single document.