Type Alias CommandFn 

pub type CommandFn = fn(&dyn Snapshot, &[String]) -> Outcome;

A command body.

Reads through the counter, returns slips. There is no &mut in this signature, which is the point: a command cannot reach editor state, so it cannot corrupt it. It replaces fn(&mut EditContext, &[String]), whose &mut BufferSet was simultaneously too much power and too little reach — the runtime still had to special-case :noh because EditContext could not see SearchState.