🚀 go-pugleaf

I'm trying to figure out where copies are "guaranteed" to exist and/or 
not to exist in C++, and I'm getting very confused.  See Dec. JCLT for related
ANSI-C issues.

Part of the problem is that "copy" can be both a noun or verb thing.  
A "copy" can mean an invocation of a copy constructor, it can mean a
separate region of memory, or it can mean both.

The issue is important for "object oriented" - style programming where
polymorphism and identity is important.  Programmers must be able to
"guarantee" in some situations that a copy is/is-not  generated, so that the
tests based on identity will work "correctly."  In this sense, a "copy" means
a distinct region of memory.

Some questions:

When a function returns-by-copy, is the region of memory that copy 
resides in distinct? [bottom of ARM page 288 seems to be implying that
C++ does indeed return-by-copy, but I guess one could even question that]

When, if ever, is it legal to invoke a copy constructor where
the source and destination memory locations are identical?

When, if ever, is it legal to invoke a copy constructor where
the source and destination memory locations are partially overlapping?

When, if ever, is it legal to have partially overlapping references
to the same object?

[please quote your sources when answering these questions]

[note that most of these questions could be applied separately for
 compiler-initiated actions [temporaries] and for programmer initiated
 actions, but I'm assuming that which a compiler is allowed to do,
 the programmer is allowed to do, and vice-versa]