To prevent potential conflicts between parallel personalizations, Unless introduced a priority mechanism.
With Unless, you can segment your customers into audiences. Just like in real life, a website visitor may be part of several audiences at the same time. This means that multiple personalizations may fire at the same time. The good news is that every single website visitor sees their own, unique version of your website - tailored to them specifically. Without a lot of work, and even if you have a lot of traffic.
There is a catch, though. In theory, personalizations may be trying to adapt the same element on the same page. To prevent such conflicts, Unless introduced a prioritization method for personalizations, in which only the most important personalization can change an element.
It works like this. When creating a personalized content snippet on a web page, this personalization must be prioritized with respect to the other personalization on that page. You can do that by dragging the personalization to the right position in a list that contains all personalizations on that page. If, by any chance, personalizations would conflict, the higher ranked personalization will execute first and lock the changed element. This element can then no longer be changed by any lower ranked personalization.
For the techies: before a personalization is applied to any element, we will look for locked child elements or locked parent elements. If we find either one of those, we will not apply the personalization.
You can find this feature in the detail view of each personalization. One more thing, though: multi-page personalizations always have a lower priority than personalizations that execute on one page only. The reason is that they are by definition less specific.