I quite agree.Unicode probably shouldn't impose any such requirement, the missing glyph is not part of Unicode and is not mapped to any character.
The purpose and semantics of the missing glyph are: 'this is the glyph that will be displayed by every application when the font in use lacks a glyph assigned to the code point being called.'
Any other use of the missing glyph would be illegitimate and it
would also be highly misleading.
Displaying either the specific missing glyph indicator in a particular font (most often an open rectangle) or displaying the glyph associated with U+FFFD would be misleading.
But in fact applications aren't consistent in their use of these or in the use of "?" as yet a third way of indicating a glyph that the application can't reproduce.
Probably the best solution would be to display a special glyph with the meaning "character not supported".
Jim Allan
Please see http://www.microsoft.com/typography/otspec/recom.htm ... the section about "Shape of .notdef glyph"
Best regards,
James Kass .
