Pathname#world_writable?

If the entry at the path in self exists and is writable by others, returns the integer permissions for the entry; otherwise, returns nil:

pn = Pathname('/tmp/t.tmp')
pn.world_writable?                        # => nil    # Non-existent.
pn.write('foo')                                       # Create file.
pn.world_writable?                        # => nil    # Not world-writable.
pn.chmod(0o777)                                       # Make world-writable.
pn.world_writable?.to_s(8)                # => "511"  # World-writable.
pn.delete                                             # Clean up.
Pathname('/tmp').world_writable?.to_s(8)  # => "777"  # Directory.