Describes POSIX file permissions, where the user, group, and others are each assigned read, write, and/or execute permissions.

The toString method provides a 9 character string where the first three characters indicate user permissions, the next three group permissions, and the final three others permissions. For example, rwxr-xr-- indicates the owner has read, write and execute, the group as read and execute, and others have read.

The value field encodes the permissions in the lowest 9 bits of an integer. bits 8-6 indicate read, write, and execute for the owner, 5-3 for the group, and 2-0 for others. rwxr-xr-- has the integer value 111101100 = 492.

The toOctalString method returns the a 3 digit string, where the first character indicates read, write and execute for the owner, the second digit for the group, and the third digit for others. rwxr-xr-- has the octal string 754.

Constructors from strings, octal strings, and integers, as well as explicitly enumerating permissions, are provided in the companion.