code: func ParseHeaderLine(line []byte) (k, v []byte, ok bool) {
  	colon := bytes.IndexByte(line, ':')
  	if colon == -1 {
  		return
  	}
  	k = trim(line[:colon])
  	for _, c := range k {
  		if !OctetTypes[c].IsToken() {
  			return nil, nil, false
  		}
  	}
  	v = trim(line[colon+1:])
  	return k, v, true
  }
docs: // ParseHeaderLine parses HTTP header as key-value pair. It returns parsed
  // values and true if parse is ok.