Gaiji is a Japanese word meaning foreign character or foreign word. It was originally used to mean characters or sounds (e.g. "London") that do not have a native kanji representation. It is commonly overused, abused, or misused in Japanese EPUB documents, and I think it should be addressed in the Alt Techniques document.

My suggested text is:

"""
1. When gaiji is used as a "hack" to display a character that is adequately represented by a real unicode character, the recommended practice is to remove the gaiji image and just use the unicode character.

2. When gaiji is used to display a character that is not available in a particular font, the alternative text should be the unicode character.

3. When gaiji is used to represent a graphical image similar to those displaying emoji, use a short description of the image's content (e.g. "thumbs up", "sunrise", or "smiling woman").

4. When gaiji is used to represent a new or made-up character that has no unicode representation, use the phonetic hiragana or katakana string to represent the pronunciation of the new or made-up character.
"""