A file reader placeholder, expression similar to calc, restricted to loading files from the .minecraft folder.
Example: {"placeholder":"file", "values": {"last_line":"true", "location":"fileposition"}}
Example usage: log-reader in loading screens

I'm pretty sure reading a file every tick to update the placeholder for getting the current last line would kill performance.

What if it was set to every second, or a user-set delay? I'm sure it wouldn't hurt that bad.