> Note that the "magic" md5 are the first four
> lowercase hex-digits of the query string md5sum, if
> you want to recompute them by hand. (an
> implementation of md5 is included in RFC 1321, if
> needed)

Additional notes:

- the md5 is empty when the query string is missing, and the string given to
md5sum is the string after the '?' (not including the '?' character itself)

- default naming pattern is "%h%p/%n%q.%t" ; %h for the host, %p for the host
path without final segment (a segment is separated by '/'), %n for the
filename without extension (the filename is the last segment), %q for the
magic md5 (or empty if no query string present) and %t for the filename
extension.

Note that the "host" is the hostname for http links (ie.
<http://www.example.com> => www.example.com), and the scheme+host for other
protocols (https://www.example.com => <https://www.example.com>, or
<ftp://ftp.example.com> => <ftp://ftp.example.com>)

- The following characters are replaced by '_' (underscore):
~,\,:,*,?,",<,>,|,@
- All characters <32, and the character 127 are also replaced by '_'
- The "//" pattern is replaced by "_/" (useful when the host part contains the
scheme)
- The "./" pattern is replaced by "_/"
- The " /" pattern is replaced by "_/"