Visibility

If a name begins with an upper-case letter, it is exported (PascalCase).
Any unexported (camelCase) names are not visible or accessible from outside the package.

There are no access modifiers such as public or private.

Internal packages

Put code which should not be used outside the program in a directory named internal.

Go 1.4 release notes: https://golang.org/doc/go1.4#internalpackages