Feature request: Placeholders with Tab Navigation

[kctdfh]

Hey! Thanks for massCode and this - exactly what I've been looking for!

I know the project is fresh and you may already have this on the roadmap but it'd be nice to have snippet placeholders that get focused by default and can be tabbed through after adding a snippet. I don't know how it could be elegantly implemented since I only write Javascript in VSCode so something like %%default value%% would perhaps conflict with the syntax of some other languages but something like that would be great.

Cheers!