It's not wise to generalise, but for the example I used above:
Originally Posted by ITA
...
Stopover restrictions
UNLIMITED STOPOVERS PERMITTED IN EACH DIRECTION IN UNITED
KINGDOM AT EUR 200.00 EACH.
CHILD/INFANT DISCOUNTS APPLY.
A STOPOVER MAY NOT EXCEED 10 DAYS.
Of course, you should check the specific routes you are interested in.