BACKGROUND According to Unicode Standard Annex #11(UAX #11) [EAW], some characters are classified as East Asian Ambiguous (A) Class. Class A characters can be sometimes wide (1 Em wide) and sometimes narrow (1/2 Em wide). Quotes from UAX#11, Section 4: Ambiguous characters occur in East Asian legacy character sets as wide characters, but as narrow (i.e. normal-width) characters in non-East Asian u