13 which may be an octal number or a symbolic change to the existing mode.
29 execute (search in directory) by owner
32 read, write, execute (search) by group
35 read, write, execute (search) by others
50 (for user's permissions),
84 is any combination of the letters
99 Only the owner of a file or the group leader of its group
100 may change the file's mode.
102 .B /sys/src/cmd/chmod.c