-The only currently support option is gz[=<compressionlevel>], to
-indicate that the whole stream should be compressed with gzip. The
-compression level defaults to 1.
+Options supported:
+
+ gz[i][=<compressionlevel>]
+ Indicates that the whole stream should be compressed with gzip.
+ The compression level defaults to 1 if gz is specified by the
+ level isn't. gzi appliies only to the incrementals; gz applies to
+ both unless gzi is also specified. compression level 0 means not
+ to run gzip at all and is the default if gz[i] is not mentioned.
+
+ snap=<snapkind>
+ Indicates that the filesystem should be frozen before the backup
+ by using /etc/chiark-backup/snap/<snapkind>. See the head comment
+ in /etc/chiark-backup/snap/lvm for details of how this works.
+ When snap= is used, the block device must be specified.
+
+ noinc
+ Suppress incrementals.