I'm using "ℏ" in a MathML formula. When making a PDF from my XHTML, I get a warning:
prince: warning: no glyphs for character U+FE00, fallback to '?'
and I indeed get a '?' right after the glyph (so the planck-glyph itself renders correctly).

This is due to line 7366 of xhtml-math11-f.dtd:
<!ENTITY planck "&#x0210F;&#x0FE00;" ><!--/hbar - Planck's over 2pi -->

Should that "&#x0FE00;" be there? If so, how can I fix the problem that it's not interpreted/rendered correctly?

(My font is Latin Modern, but I get the same with Times New Roman. UTF-8 encoding. Prince 9, Mac OS 10.8.)

U+FE00 is a variation selector, which Prince currently just treats as a regular character and cannot find a glyph for it. I'm not sure why it would be necessary, as not many systems use variation selector characters in practice. Removing it from the DTD seems like the best solution.

Ah, okay, I'll do that. Thanks!