Every folder can have an permission file: "__access__.yaml"
The files are in YAML: an python-like data structure.
# every folder has an owner.
# if this is not defined, it inherits
# an valid __access__.yaml file always includes an owner
owner: <name>
# every folder can have per-user access rules (see format below)
users:
<username>: <permissions>
...
# every folder can have per-group rules as well
groups:
<groupname>: <permissions>
...
# and last: per-file rules (advanced)
contents:
<relative/path/to/item>:
# also has per-user rules
users:
<username>: <permissions>
...
# and group rules
groups:
<groupname>: <permissions>
...