Outstanding and helpful reply, folks. As far as the suggestion about leaving the fonts up to the user, I think I’ll go with the url('res:///Data/fonts/foobar.ttf') scheme, storing the fonts on the Reader itself, instead of packing them inside the ePub, unless there’s a pressing need for something custom... even then, if it’s a one-off instance, I could just convert the type to outlines and embed it as a SVG. Makes for a drastically smaller ePub when you're using fonts with a lot of glyphs, as well.
— @yg
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