In building a general purpose guideline system based on GLIF--the GuideLine Interchange Format, we encountered limitations in the GLIF specification. These limitations, while not so apparent in the static version of guideline content, became readily so in the context of real world implementation, and pertain not only to GLIF-based systems, but generally as well. These limitations can be described as being in one of five categories. In this paper, we describe each of these categories in detail, and show how an execution environment based on XML data structures addresses these concerns.