Tests if @hostname contains segments with an ASCII-compatible encoding of an Internationalized Domain Name. If this returns %TRUE, you should decode the hostname with g_hostname_to_unicode() before displaying it to the user.
Tests if @hostname is the string form of an IPv4 or IPv6 address. (Eg, "192.168.0.1".)
Tests if @hostname contains Unicode characters. If this returns %TRUE, you need to encode the hostname with g_hostname_to_ascii() before using it in non-IDN-aware contexts.
Converts @hostname to its canonical ASCII form; an ASCII-only string containing no uppercase letters and not ending with a trailing dot.
Converts @hostname to its canonical presentation form; a UTF-8 string in Unicode normalization form C, containing no uppercase letters, no forbidden characters, and no ASCII-encoded segments, and not ending with a trailing dot.