NULL vs. `infinity` in PostgreSQL range types

Question

What is the meaning of \'infinity\' in PostgreSQL range types? Is there any difference between specifying infinity or -infinity as a bound, or

Answer 1

NULL does the same thing for the overlap operator && as -infinity or infinity, respectively. I quote the manual here:

Using NULL for either bound causes the range to be unbounded on that side.

But as value, NULL is still distinct from 'infinity'!

SELECT tstzrange('-infinity','infinity') = tstzrange(NULL, NULL);

Returns FALSE (not NULL, mind you!).

More in this SQLfiddle.