Function explain 

pub fn explain(resolved: &Resolved, key: &str) -> Option<String>

One setting explained: what it is, where it came from, and what else tried.

jobs = 4
  set by  MISE_JOBS
  type    uint

  also considered, lowest precedence first:
    the default
    mise.toml#jobs

Returns None for a key the registry does not have, which the caller reports its own way — a CLI usually wants to suggest a near miss, and this module has no business guessing.