To differentiate a pure consonant ("chillu") and a consonant with "ŭ", zero-width joiner (ZWJ) and zero-width non-joiner (ZWNJ) were used before Unicode 5.1. However, this system was problematic. Among other things, glyph variants specified by ZWJ or ZWNJ are supposed to be non-semantic, whereas a "chillu" (expressed as letter + virama + ZWJ) and the same consonant followed by a "ŭ" (expressed as letter + virama + ZWNJ) are often semantically different. After a long debate, Nine "chillu letters" now have their own code points since Unicode 9.0, though applications should also be prepared to handle data in the representation specified in Unicode 5.0. This means, fonts should display chillus in both sequences; while an input method should output standard chillus.