When there is no font for a character (e.g. prince: warning: no glyphs for character ... fallback to '?') could you possibly remove the character? That would look better than long strings of ??????????????? which tend to mess up the PDF.

You can do this with:

prince-text-replace: 'a' ''

where 'a' is the character you don't have glyphs for.

Thanks, Mike. That would be a great solution for the characters that I know about. Unfortunately, there are thousands I don't know about since I'm doing multilingual PDFs. For those it would be great if Prince didn't change the character to a "?".

That could lead to bizarre output, with words or parts of words missing in unexpected places. The way Prince is designed at the moment it has to use some glyph for unknown characters, and '?' seems like a reasonable choice.

I understand your point. But isn't the word missing whether you use "??????????" or zero-space characters? The only different is that in one case everyone notices the error (and the PDF may be rejected for quality reasons) and in the other case it goes largely unnoticed. Just a suggestion.

Yes, but the idea is to notice the error, and then correct it by using a suitable font.