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" />


viz: http://www.stoa.org/projects/epidoc/snapshot/guidelines/notations.html

FWIW,

Tom


Tom Elliott, Ph.D.
Director, Pleiades Project
Ancient World Mapping Center
University of North Carolina at Chapel Hill
http://pleiades.stoa.org