OTOH domino or mahjong tiles (🁓, 🀕), playing cards (🃅) or musical symbols (𝅗𝅥) are allowed. So are arrows (↸) including supplementals (⤪), number forms (ↈ), superscripts and subscripts (⁴₂), "miscelllaneous technical" (⎋, ⏱) or geometric symbols (◉), however misc symbols (https://en.wikipedia.org/wiki/Miscellaneous_Symbols) is a no.

So yeah, pretty arbitrary. I guess pg likes playing domino but hates chess.

Also funny note: we have access to musical symbols but not notes, because the notes are in the misc. symbols block. Unless you want to use byzantine (𝀶) or ancient greek (𝈙) musical notation then it's OK.