- create mask (default: 0744)
When a file is created, the necessary permissions are calculated
according to the mapping from DOS modes to UNIX permissions, and
the resulting UNIX mode is then bit-wise 'AND'ed with this
parameter.
- directory mask (default: 0755)
This parameter is the octal modes which are used when converting
DOS modes to UNIX modes when creating UNIX directories.
Thank you. I believe this is saying something like idea 1 from my question. The mask may "limit" but does not "take away."
So if the "resulting UNIX mode" is 770 and the create mask is 744, an "AND" operation would give us 740?
Because "AND" means permitting only what is permitted in both the "resulting UNIX mode" AND the create mask?
That's my totally random guess from the context. It's hard for me search for "AND" because it is such a common word.
Of course I also don't know how one comes up with the "result UNIX mode" because I don't know where one gets the "DOS modes," but that I can worry about later.