Ar an tríú lá is fiche de mí na Samhain, scríobh David Kastrup: > > I have a tentative plan to add a charset to XEmacs, 256 > > characters of which reflect corrupt Unicode data. These 256 > > characters will be generated by Unicode-oriented coding systems > > when they encounter invalid data: > > > > (decode-coding-string "\x80\x80" 'utf-8) > > => "\200\200" ;; With funky redisplay properties once display tables > > ;; and char tables are integrated. Which, whee, is more > > ;; work. > > Here is what Emacs 22 returns: > > #("\xc2\x80\xc2\x80" 0 2 (display #("\\200" 0 4 (face escape-glyph)) help-echo utf-8-help-echo untranslated-utf-8 128) 2 4 (display #("\\200" 0 4 (face escape-glyph)) help-echo utf-8-help-echo untranslated-utf-8 128)) > > > And will be ignored by them when writing: > > > > (encode-coding-string (decode-coding-string "\x80\x80" 'utf-8) 'utf-8) > > => "" > > Here is what Emacs 22 returns: > > "\200\200" Quite an old GNU Emacs 23.0.0 gives me this: (encode-coding-string "\x80\x80" 'utf-8) => "\200\200" (decode-coding-string "\x80\x80" 'utf-8) => "\200\200" Savannah’s being unco-operative about allowing me to cvs update, otherwise it would be worth reporting the former as a bug.

Were it my implementation, I would regard the latter as a bug too.

> > This will allow applications like David Kastrup’s reconstruct-utf-8 > > sequences-from-fragmentary-TeX-error-messages to be possible, while > > not contradicting the relevant Unicode standards. With Unicode as > > the internal encoding, there’s no need to have a separate Mule > > character set; we can stick their codes somewhere above the astral > > planes. But we should maintain the same syntax code for them. Note > > also that, as far as I can work out, these 256 codes will be > > sufficient for representing error data for all the other > > Unicode-oriented representations well as UTF-8. > > Not just for "unicode-oriented". The recipe should be workable for > the iso-latin-* stuff as a file encoding, too, I think. Hmm? _Are_ there invalid sequences for the ISO-8859-N file encodings?