thread linking forum function?

[Bob]

It might be useful if it were easy to link threads together when you spin-off an idea from one thread. 

For example, you think of a slightly off-topic idea while viewing or replying to a thread.  It would be nice to be able to link them together. 

I've tried it in places like this, but it's a bit of a pain to set up.
https://pianoforum.net/smf/index.php/topic,7382.msg73539.html#msg73539


Or is there already a function like this that I don't know about?