Use the SIL Unicode BMP Fallback Font

[davelab6]

The font stack should have the SIL UBF Font as the 2nd in the stack, so glyphs not present are visible.

http://typedrawers.com/discussion/50/drag-and-drop-font-testing-page#latest

[moyogo]

An alternative would be to have Adobe Blank https://github.com/adobe-fonts/adobe-blank/ http://sourceforge.net/adobe/adobe-blank if the user prefers having blank missing glyphs instead of informative codepoint glyphs.

[davelab6]

Yes, both should be options available in what is now the 'OpenType' features dropdown