[XeTeX] protrusion for small caps

[Robert]

Hi,

I'm having problems with setting protrusion values for small caps. The 
following does not give the desired result. Any hints?

\font\x ="Charis SIL:+smcp" \x
\hsize=11em
\parindent=0pt
\XeTeXprotrudechars2
\lpcode\x U`W = 500 % this works fine,
% but neither of the following does:
\lpcode\x U`w = 500
\lpcode\x U"1D21 = 500
\lpcode\x 2310 = 500 % according to Character Palette
\lpcode\x /Wsmall = 500 % just guessing

abcdef abcdef abcdef
Wbcdef abcdef abcdef
wbcdef abcdef abcdef
abcdef abcdef abcdef
\bye

Regards,
-- 
  Robert