A updated version.

[Yonggang Luo]

I have a file that named 
baseClass.d
The content is
module baseClass;

public class Base
{
}

public void Function()
{
}


private class BaseAlternative
{
}

private void FunctionAlternative()
{
}

And the other file that named
subClass.d
The content is
module subClass;
private import baseClass; /*!!!!!!!! Please notice, this is private import*/

class Sub:Base /*Is this legal?*/
{
};


void DoSomeThins()
{
	Function(); /*Is this legal?*/
}


private void DoPrivateFunctions(Base x) /*Is this legal?*/
{
}

public void DoPublicFunctions(Base x) /*Is this legal?*/
{
}

private alias Base BaseAlternative; /*Is this legal?*/

public alias Base PublicBase; /*Is this legal?*/