Apple renamed "Mac OS X" to "macOS" in 2016.
* Replace instances of "OSX"/"OS X"/etc. with "macOS" in comments to reflect the change.
* There are additional references to things like "osx" in functional code which are left unchanged.
* Grammatical changes due to the initial letter changing from a vowel to a consonant (o => m) in some places.
* Fix a unrelated minor grammatical issue.