What is the "Link id" constraint in the smart list filter "Clicked link in email"?
Just noticed this today. Anyone who knows what it is? I now it's possible to tag links in emails in some other ESPs which tags/ids etc., which can then be used to segment on, so you don't have to know exactly all URLs for e.g. segmenting on a product interest by a link click - could you use it for this?

