One issue I ran across while learning jquery was that I often wanted/ needed a way to tell jquery to get data for the current element from a related element. jQuery immediately tends to be friendly when you need to work with a class of elements via the CLASS attribute, or a specific element via the ID attribute. However, when there are 2 elements that are related but do not fit within a class, a beginner such as myself may have a little trouble trying to find the best way to handle this issue. At this point we begin to research how to get jQuery to recognize a custom attribute, because common rules says that the ID attrib is basically out of the question as this needs to be unique to each element. And the CLASS attrib just doesn't logically help either because it can refer to too many other elements that don't fit our rule. And when we find out that jQuery doesn't readily recognize custom attributes it can get a little intimidating because one of the solutions is to extend jQuery. But there are a couple of other standard attributes that are recognized but rarely used. In my particular case I started using the TITLE attribute for relating my elements. But then I stumbled upon the correct way, (or at least until someone corrects me on this post). There is a REL attribute which can be used to RELATE the to elements. So when you feel like you need a custom attribute, you might not need one, the REL is available and the TITLE could be used as a backup if necessary.
I hope this helps someone.