James Robinson wrote:

Can I use a round trip ticket as a 1 way?

Yes, you can do that. Just make sure it is the first flight
that you take, and not the second. If you miss the first flight,
the rest of you reservation will be canceled.

I'm not questioning the common belief of the above paragraph. But
this made me wonder if (or where) that stipulation is documented /
printed. Anyone care to read the fine print on their latest ticket
and confirm?

Is such a disclaimer visible when you buy tickets on-line (given that
as the majority of tickets are e-tickets there is increasingly no
fine-print on your ticket at the time of purchase because there is no
ticket anymore).