-.B CALLOUT
-calling external program, that returns a string to match. The
-.BR BUS
-key is optional, but if specified, the sysfs device bus must be able to be
-detemined by a "device" symlink.
-.br
-.RB "keys: " BUS ", " PROGRAM ", " ID
-.TP
-.B LABEL
-device label or serial number, like 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. The
-.BR BUS
-key is optional, but if specified, the sysfs device bus must be able to be
-detemined by a "device" symlink.
+.B BUS
+Match the bus type of the device.
+(The sysfs device bus must be able to be determined by a "device" symlink.)
+.TP
+.B KERNEL
+Match the kernel device name.
+.TP
+.B ID
+Match the device number on the bus, like PCI bus id.
+.TP
+.B PLACE
+Match the topological position on bus, like physical port of USB device
+.TP
+.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 to match the rule.