That's not a good name for the flag.  The problem is that 'read-only' means different things on Windows than it does on Unix.  Which is why I suggested that the flag control whether or not it acts "posix like" on Windows.  So perhaps 'posix_compat'?  That feels a bit odd, though, since on posix it does nothing...so it's really about behavioral consistency across platforms....

Hmm.  It's really hard to think of a name that conveys succinctly what we are talking about here.

A more radical notion would be something like 'delete_control' and have it be tri-valued: 'unixlike', 'windowslike', and 'native', with the default being native.  Bad names, most likely, but you get the idea.  The disadvantage is that it would be even more code to implement ;)