How can I add a custom compose key sequence?

For example, I would like Compose, |, > to type the ▸ symbol.

I have tried adding the following to ~/.XCompose:

# Import default rules from the system Compose file

include "%L"



# Custom definitions

<Multi_key> <bar> <greater> : "▸" U25B8 # Black right-pointing small triangle

but the new sequence is not usable anywhere except for xterm.

Installing ibus-table-compose and then enabling the Compose input method in IBus did not solve the problem; IBus imitated many compose key sequences, but not the one I had created.