<algorithm>=<hexdigits>
<algorithm> identifies the checksum algorithm used, and allows new
-algorithms to be added later. At the moment, the only permissible value
-is "sha1", indicating a SHA-1 checksum.
+algorithms to be added later. Permissible values are:
+ "sha1": SHA-1
+ "sha224": SHA-224 (added in version 0.11)
+ "sha256": SHA-256 (added in version 0.11)
<hexdigits> is a sequence of hexadecimal digits which encode the
checksum value. For sha1, <hexdigits> should be precisely 40 digits