Why public/open access level specified with swift classes?

[shubham101096]

In this project, all the classes which are written in swift and are used by objective c files have been declared as public/open. Even their functions and variables which are used by objective c files have been declared public/open. Is it necessary to declare the classes/their functions public in order to be accessed by objective c classes? Because in apple documentation I could not find any such rule.
Eg: ServerCapabilitiesViewController class has been declared public and it also has a public init method. Could it also had been declared without any explicit access level?