further tweak addr_of exposition

Author: RalfJung

Diff for: src/expressions/operator-expr.md

@@ -82,10 +82,10 @@ let a = & & & & mut 10;
 ### Raw address-of operators
 
 Related to the borrow operators are the *raw address-of operators*, which do not have first-class syntax, but are exposed via the macros `ptr::addr_of!(expr)` and `ptr::addr_of_mut!(expr)`.
-Like with `&`/`&mut`, the expression `expr` is evaluated in place expression context.
-The difference is that `&`/`&mut` create *references* of type `&T`/`&mut T`, while `ptr::addr_of!(expr)` creates a (const) raw pointer of type `*const T` and `ptr::addr_of_mut!(expr)` creates a mutable raw pointer of type `*mut T`.
+The expression `expr` is evaluated in place expression context.
+`ptr::addr_of!(expr)` then creates a (const) raw pointer of type `*const T` to the given place, and `ptr::addr_of_mut!(expr)` creates a mutable raw pointer of type `*mut T`.
 
-The raw address-of operators must be used whenever the place expression could evaluate to a place that is not properly aligned or does not store a valid value as determined by its type.
+The raw address-of operators must be used instead of a borrow operator whenever the place expression could evaluate to a place that is not properly aligned or does not store a valid value as determined by its type, or whenever creating a reference would introduce incorrect aliasing assumptions.
 In those situations, using a borrow operator would cause [undefined behavior] by creating an invalid reference, but a raw pointer may still be constructed using an address-of operator.
 
 The following is an example of creating a raw pointer to an unaligned place through a `packed` struct: