code: func (c *Connection) checkClientVersions(h Headers) (e error) {
  	w := h.Value(HK_ACCEPT_VERSION)
  	if w == "" { // Not present, client wants 1.0
  		return nil
  	}
  	v := strings.SplitN(w, ",", -1) //
  	ok := false
  	for _, sv := range v {
  		if hasValue(supported, sv) {
  			ok = true // At least we support one the client wants
  		}
  	}
  	if !ok {
  		return EBADVERCLI
  	}
  	if _, ok = h.Contains(HK_HOST); !ok {
  		return EREQHOST
  	}
  	return nil
  }
docs: /*
  	Check client version, one time use during initial connect.
  */