code: func GetEncoding(charset string) encoding.Encoding {
  	charset = strings.ToLower(charset)
  	encodingLk.Lock()
  	defer encodingLk.Unlock()
  	if enc, ok := encodings[charset]; ok {
  		return enc
  	}
  	switch encodingFallback {
  	case EncodingFallbackASCII:
  		return gencoding.ASCII
  	case EncodingFallbackUTF8:
  		return encoding.Nop
  	}
  	return nil
  }
docs: // GetEncoding is used by Screen implementors who want to locate an encoding
  // for the given character set name.  Note that this will return nil for
  // either the Unicode (UTF-8) or ASCII encodings, since we don't use
  // encodings for them but instead have our own native methods.