I'm trying to add a custom glyph to a font. I go to Encoding > Add Encoding Slots > press OK for 1 slot. Then I open up the window for the new glyph and I paste the new glyph in there. I generate the font and then I modify my html and write 𐀊 which should refer to the newly-created glyph. But when I run it in the browser it doesn't show (just get the box with a question mark inside it). The way I'm referencing it, using that number, works for all the existing glyphs. So what am I doing wrong / failing to do?