+ * The possible priority classes. Possible values are, in order of descending
+ * priority: <code>maximum</code> (anything more important than fproxy),
+ * <code>interactive</code> (fproxy), <code>semi-interactive</code> (fproxy
+ * immediate mode large file downloads, not to disk), <code>updatable</code>
+ * (updatable site checks), <code>bulk</code> (large file downloads to disk),
+ * <code>prefetch</code>, <code>minimum</code>.
+ *