OK, so if looks as if I am going to have to use \loop \if \repeat in conjunction with \XeTeXcharclass ‹char slot› [=] ‹interchar class› to set up the XeTeX char class for polytonic Greek, but looking at Charmap for Palatino Linotype it would seem as if at least two non-contiguous ranges will be needed (maybe more). Are there any standard modules that can be used to set this up (remember : XeTeX, not XeLaTeX), and/or are these ranges easily located from the Unicode documentation ? We'll pass on Hebrew for now :)
** Phil.