These are extensions added for better interop with the embedded emulator.
As characters inside the unicode private-use area, you shouldn't encounter
them unless you opt in by using some other proprietary feature.
If you use Terminal.requestSetTerminalSelection, you should also process
this pseudo-key to clear the selection when the terminal tells you do to keep
you UI in sync.
These are extensions added for better interop with the embedded emulator. As characters inside the unicode private-use area, you shouldn't encounter them unless you opt in by using some other proprietary feature.