code: func (e Env) Iter(cb func(k, v string) bool) {
  	e.iterate(func(_, k, v string) bool { return cb(k, v) })
  }
docs: // Iter iterates through all of the key/value pairs in Env and invokes the
  // supplied callback, cb, for each element.
  //
  // If the callback returns false, iteration will stop immediately.