gistfile1.txt

[1234] means 1234 represented on 32 bits
# indicates a comment
We escape:
- \ as \\
- character 0 as \0
- literal [, ] as \[, \]
- classical \ (\->\\, char 0 as \0, etc.)
- # as \#

lexicon:
S step
F file (contains errnos on operations)
D file data
S file stat
C command (contains errnos on execution)
O command stdout
E command stderr
? command return code
/ number of subitems (used for steps, files that are directories)

S\0/ -> [5]
S\0[0] -> Sgeneral\0
S\0[1] -> Skernel\0
S\0[2] -> F/etc/puppet/puppet.conf\0
S\0[3] -> ...
S\0[4] -> ...
Skernel\0/ -> [2]
Skernel\0[0] -> Skernel/mem\0
Skernel\0[1] -> Skernel/io\0
Sgeneral\0/ -> [1]
Sgeneral\0[0] -> Cdf\0
Skernel/io\0/ -> [1]
Skernel/io\0[0] -> F/etc/puppet/puppet.conf\0 # we read that earlier in execution

F/etc/puppet/puppet.conf\0 -> [0][0] # we didn't meet any errno when running stat or reading
S/etc/puppet/puppet.conf\0 -> [12][53][189]... # a struct stat serialized in a straightforward, platform independent way. shows it's a standard file, hence has contents in data
D/etc/puppet/puppet.conf\0 -> blahblahblah # file contents
F/etc/nfs\0 -> [0]
S/etc/nfs\0 -> ... # shows it's a symlink
D/etc/nfs\0 -> /etc2/nfs # readlink
S/etc2/nfs\0 -> ... # shows it's a directory
F/etc2/nfs\0 -> [0][0][0]...[0][4][6] # we met errnos 4 and 6 during readdir
F/etc2/nfs\0/ -> [9] # 9 dirents were readdir'ed
F/etc2/nfs/\0[0] -> ... # a dirent serialized in a straightforward, platform independant way :) includes the filename, eg "foo"
F/etc2/nfs/\0[8] -> ...
F/etc2/nfs/foo\0 -> [0]
S/etc2/nfs/foo\0 -> ... # shows it's a regular file
D/etc2/nfs/foo\0 -> <bar>\n</bar>

Cdf\0 -> [0] # no errnos when executing or reading the output
?df\0 -> [0] # return code for the command
Odf\0 -> Filesystem    512-blocks      Used Available Capacity  Mounted on\n/dev/disk0s2   117817264 116922808    382456   100%    /
Edf\0 -> \0

by "contents" I mean "children".
you will have guessed that we prefix every string by its length in keys.