+.BI SYSFS{ filename }
+Match sysfs device attribute like label, vendor, USB serial number, SCSI UUID
+or file system label. Up to 5 different sysfs files can be checked, with
+all of the values being required in order to match the rule.
+.TP
+.B PROGRAM
+Call external program. This key is valid if the program returns successful.
+A few command line options may specified, but shell characters like pipe,
+diversion or similiar options are not available. The environment variables of
+.B udev
+are also available for the program.