I think it also uses ligatures to render words from the "phrasebook", where you can take a word like "friend" and change the font from Times to this font, and it renders it as 朋友. Beautiful.
(Font author)
This is all off the beaten path, so I suspect the answer is no one knows. Font tables have a limit of 65k characters, but this ceiling can be busted in whacky ways using multiple lookups, useExtension... Practically, font building tools / operations crash (mysteriously), stalls (mysteriously), or slows to a crawl (indistinguishable from stalling), and the Cantonese Font about pushes the limit.
Setting aside for a minute the question of whether you _should_, I wonder how far you can take this? I.e. what limits are there on how much context you can take into account, etc.?