Apple's documentation(https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AccessControl.html#//apple_ref/doc/uid/TP40014097-CH41-ID3) says: "You typically use open or public access when specifying the public interface to a framework"
What is a public interface?
And what does it mean to specify the public interface to a framework?
