code: func splitEntryGivenKey(key, entry string) (k, v string) {
  	prefixSize := len(key) + len("=")
  	switch {
  	case len(entry) < prefixSize:
  		return entry, ""
  	case len(entry) == prefixSize:
  		return entry[:len(key)], ""
  	default:
  		return entry[:len(key)], entry[prefixSize:]
  	}
  }
docs: // splitEntryGivenKey extracts the key and value components of the "env" map's
  // combined "key=value" field, given the "key" component.
  //
  // This will work as long as the length of the supplied key equals the length of
  // entry's key prefix, regardless of the key's contents which means that
  // normalized keys can be used.
  //
  // It assumes that the environment variable is well-formed, one of:
  // - KEY (returns "")
  // - KEY= (returns "")
  // - KEY=VALUE (returns "VALUE")
  //
  // If this is not the case, the result is undefined. However, this is an
  // internal function and should never encounter a situation where the entry is
  // not well-formed and prefixed by the supplied key.