I wonder if it's relevant to this discussion how epidoc is trying to
handle "a mark in the original text that is not readily handled by
conventional type or fonts (e.g., does not correspond to a Unicode code
point) but is not really an illustration."
An empty extension element with a "type" attribute, e.g.:
<mark type="claudian_ps" />
Tom Elliott, Ph.D.
Director, Pleiades Project
Ancient World Mapping Center
University of North Carolina at Chapel Hill