main is a better term to use here for several reasons:
1. It is more accurate: "master" implies that the designated views have
some kind of control over the other views, which is not the case. "main"
better expresses that the difference between the "main" view and others
is one of importance/focus.
2. It is a shorter word. 2 whole characters saved!
3. It reduces the chance of future development time being lost to
good-intentioned people complaining about usage of the word master as
has recently happened with regards to the default git branch name.
