It doesn't exist in the current XPtr spec. This means that there is no syntactic distinction between inline and out of line in XArc. There is no explicit unambiguous connectivity information. As stated, I am using directed graphs as my underlying framework for thinking about linking. Therefore, I want to be able to express all links in this manner.
Unidirectional links are trivial to map.
Bidirectional links are also straightforward. They're a pair of arcs with the two vertices interchanged. This is not the way that XLink defines them which is the start of my problem. There are three vertices here. ArborText, Inso, and Brown University.