code: func (e *Env) iterate(cb func(realKey, envKey, envValue string) bool) {
  	for k, v := range e.env {
  		envKey, envValue := Split(v)
  		if !cb(k, envKey, envValue) {
  			break
  		}
  	}
  }
docs: // Internal iteration function. Invokes cb for every entry in the environment.
  // If the callback returns false, iteration stops.
  //
  // It is safe to mutate the environment map during iteration.
  //
  // realKey is the real, normalized map key. envKey and envValue are the split
  // map value.