Flex inheritance.

Let B be a base class, E - a class extending B, and X be some random class that does not extend B nor E. By default all fields and methods in AS3 are declared internal, so if you did not provide a scope specifier for your method/field, it will be treated as internal.

Scope specifiers available in AS3:

• public methods and fields are visible to code anywhere (Both E and X have access to those).
  
• private fields and methods are visible only within the class defining them (E has no access to any private fields or methods from B, nor does X)
  
• protected fields and methods are visible to the class defining it and all subclasses (E has access to protected entities, independent of the package it belongs to, but X has no acces to them).
  
• internal methods and fields are accessible by all classes in the same package and can onlny be inherited by a class in the same package (E has access to internal only if E belongs to the same package as B, same applies for X.)
  

More detailed discussion on inheritance in ActionScript 3.0: here

To force child to show scroll bars instead of resizing the parent: set parent's minHeight = 0, height = 100% and that should do it.