Scala quiz. How would you change declaration of function <b>fo

How would you change declaration of function foo to ensure that a function foo is only accessible by classes defined in the package com.quizful ?

package com.quizful

class Foo {
   def foo = {...}
}

Explanation

Get an explanation when it's available:

Theory

Access modifiers can be augmented with qualifiers. A modifier of the form private[X] or protected[X] means that access is private or protected "up to" X, where X designates some enclosing package, class or singleton object.
```
package quizful {
   package prof {
      class Executive {
         private[prof] var details = null
         private[quizful] var friends = null
         private[this] var secrets = null

         def help(another : Executive) {
            println(another.details)
            println(another.secrets) //ERROR
         }
      }
   }
}
```
Note the following points:
- Variable details will be accessible to any class within the enclosing package prof.
- Variable friends will be accessible to any class within the enclosing package quizful.
- Variable secrets will be accessible only on the implicit object within instance methods (this).