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.