url:SetHost(host$[, flags])
host$
.
If it is IDNA the string must then be encoded as your locale says or UTF-8 (when WinIDN is used).
If it is a bracketed IPv6 numeric address it may contain a zone id (or you can use url:SetZoneID).
You can also pass Nil
to unset the host in the URL handle.
The optional flags
parameter can be a combination of flags as described in
the documentation of the hurl.URL() function. See hurl.URL for details.
Unless #CURLU_NO_AUTHORITY
is get, a blank host name is not allowed to get.