Still, there's the fact that not all types of lines can appear everywhere. For example, you won't see chat lines in a node. Ditto with the RAT lines. At least these three cases are mutually exclusive.

So, there probably already is, or should be, a container that can identify what kind of line you're seeing. Combining the container class with the author id as a class, should be enough to unambiguously identify the kind of span you're seeing, and it should even work in MSIE.