Access parameters and accessibility

["Michael B." <michaelb@example.com>]

I'm reading the book "Programming in Ada 2005" of John Barnes and I have 
difficulties to understand the chapter about access parameters.
In chapter 10.7 on pages 197/198 he writes:

---
An access parameter can be passed on to another access parameter; 
typically the accessibility indication is passed on unchanged but in the 
unusual circumstance where the called subprogram is internal to the 
calling subprogram, the accessibility level is replaced by that of the 
(statically known) formal calling parameter if less than the original 
actual parameter.
---

Could someone give an example/explanation where this rule is used?
I tried to read the RM. Chapter 3.10.2 seems to be the right one but I 
don't understand it either...

Thanks in advance,

Michael