Originally Posted by strcpy

Each skill has a "trigger" that has to be met first. If that is not done then it will not cast the skill. The AI will then tend cast the leftmost skill that is OK to cast. For instance, Echo tends to trigger after the skill with the longest recharge on your bar is cast - thus it tends to echo "reckless haste" in most spiteful spirit skill bars regardless of it's position. There is *some* intelligence there - in general your longest recharge skill is the one you want compied so that gets the highest priority (higher than leftmost skill). Somethings - like Death Nova or Jagged Bones tends to have such a high priority that they overrule everything else.

You can tell that position has quite a bit to do with it, just re-order your skills and they will cast in an entirely different manner. Especially true if you have a group of skills that are all about the same (effect, cost, recharge), then "leftmost" tends to be the major factor. For example, if you have several self heals that are about equal in power (Dervish is a good case for this) then it will go pretty much left to right in those skills as its health drops - health dropping being the trigger.

In computer science terms you have a priority queue. It examines quite a few factors, assigns skills priority, and the executes the highest one. Going left to right adds a smaller value to the priority but isn't enough to override everything else.