Unicode char comparison puzzle

[Claudio L.]

(05-30-2018 12:50 PM)tcab Wrote:  Thus it looks like the Prime cannot visually represent / print out all unicode characters, only a limited subset of them

Devices don't decide which Unicode symbols they can print, that's what fonts are for. Different fonts have glyphs for different character sets. I don't know of any font that has "all" Unicode characters, some are more complete than others but they are all mere fractions depending on usage.
Back to your problem: Code-wise, the Unicode characters don't change just because the font doesn't have a glyph to display it, therefore there's no way for you to filter the text, unless you take the font in which you want to display the text, make yourself a catalog of which characters have a glyph and which ones will display the default one, and use that table to do the filtering. Basically you need one table per font, or a program to "extract" that table from any font, and your filter code using those tables.