This talk will describe the "gaiji" requirement, survey the leading gaiji mechanisms in use by the Japanese publishing and personal computer industries, and look at the interesting light which gaiji glyphs (or are they characters?) casts on the Unicode character-glyph model.

Unicode encodes Han characters by the tens of thousands, but fonts typically have only thousands of glyphs. Some fonts may have more glyphs, some may have fewer. And since the Han character repertoire is fundamentally open-ended, there will always be characters which are not encoded. The characters legal for the script, but not in your font, are known as "gaiji". Writers and publishers insist on being able to use gaiji, so the Japanese publishing and computer industries have come up with a number of gaiji mechanisms. Looking from the viewpoint of a publishing software and font developer, we describe and evaluate a few of the most important gaiji mechanisms. Finally, we look at gaiji in terms of the Unicode character-glyph model. Are they glyph variants, or characters, or both, or neither?