-calling external program, that returns a string to match
-.br
-keys: \fBBUS\fP, \fBPROGRAM\fP, \fBID\fP
+,
+.B LABEL
+,
+.B NUMBER
+,
+.B TOPOLOGY
+,
+.B REPLACE
+.P
+The
+.B NAME
+and
+.B PROGRAM
+fields support simple printf-like string subtitution:
+.RS
+.TP
+.B %n
+the "kernel number" of the device
+for example, 'sda3' has a "kernel number" of '3'
+.TP
+.B %M
+the kernel major number for the device
+.TP
+.B %m
+the kernel minor number for the device
+.TP
+.B %b
+the bus id for the device
+.TP
+.B %c
+the CALLOUT program returned string
+(this does not work within the PROGRAM field for the obvious reason.)
+.TP
+.B %D
+Use the devfs style disk name for this device.
+For partitions, this will result in 'part%n'
+If this is not a partition, it will result in 'disk'
+.RE