Options dropdown for input characters

Hi,
Just like python’s prompt-toolkit library, is it possible then when inputting text, I can have several characters which have special drop-down for possible inputs.
For example

Let $theorem be blah-blah

So when I type $, I get a dropdown which shows, say, ["theorem", "proof", "conjecture"] I can either write whatever I want or choose one of them.

This is a very neat feature in my opinion since one might want to give LLM’s some prompt and have such references can help detection of usages of input theorem(somewhere before in UI). It can also help in typing stuff too.
If something like this exists, please share!

Thanks in advance!