Determines if a character is typically rendered in a double-width cell under legacy East Asian locales. If a character is wide according to g_unichar_iswide(), then it is also reported wide with this function, but the converse is not necessarily true. See the Unicode Standard Annex #11 for details.
If a character passes the
g_unichar_iswide() test then it will also pass
this test, but not the other way around. Note that some characters may
pass both this test and g_unichar_iszerowidth().