This argument does not hold water. Simply because some images appear in some documents does not mean that they automatically should be represented as encoded characters. Many images are not appropriate for use in plain text, or have too small a user community. They should be represented as private use characters, or as literal images. The Prince glyph, on-beyond-zebra characters, the images on images on http://www.aperfectworld.org/animals.htm, etc. are in quite a number of documents, but that doesn't mean that any of them necessarily qualify as characters for encoding.
Mark, come on. Doke's phonetic transcription of !Xung is a set of explicit glyphs representing specific sounds, indeed more precisely than IPA allows (I don't think IPA specifies a representation for retroflex clicks). Apart from the question whether or not the characters are important enough for people to want to be able to interchange them as encoded UCS characters (which is stipulated as a question), it's just not on to say that these are the same kinds of things as Prince's logo or the Seussian extensions.
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Michael Everson * * Everson Typography * * http://www.evertype.com
