On 27 April 2015 at 01:05, Douglas McKenna <d...@mathemaesthetics.com> wrote:
> Joseph Wright wrote: > > > \def\"{0}\expandafter\def\csname^^^^^00022\endcsname{1} > > \ifnum\"=0 \message{tex82}\else\message{newstuff}\fi > > When I implemented a Unicode escape sequence extension using double-caret > notation in the JSBox TeX-language interpreter I've been working on (which > is all 21-bit Unicode internally, all the time, but can be configured at > run-time to be 8-bit input only), I was unaware of what XeTeX had > implemented, so I just used > > ^^uxxxx (for 16-bit, BMP codes) > ^^Uxxxxxx (for all 21-bit Unicode code points) > > Seemed straightforward enough. > Introducing incompatible syntax for functionality shared across Unicode TeX extensions is a major headache for package authors. Please don't use this syntax! > > In the first case, if any one of the four 'x's is not a lowercase hex > digit, interpretation reverts to the standard TeX escape sequence ^^u > (ASCII '5'), followed by four input characters, at least one of which is > not a hex digit. Similarly for the six hex digit case, for whatever > character ^^U converts to, if at least one of the six characters following > is not a hex digit. > In the abstract this isn't an unreasonable syntax but ^^^^,^^^^^,^^^^^^ has been in use for years in xetex and luatex. > > Given that the number of TeX input files using ^^u is likely miniscule, > and the number of those that follow the ^^u or ^^U with four or six hex > digits is even smaller, it seemed like a worthwhile benefit vs. cost, > compatibility-wise. Maybe there's something I've not thought out well. > Incompatible syntax makes supporting cross platform formats like latex much more difficult than it would otherwise be, > > This discussion I just found is both pertinent and frightening, I suppose: > > http://stackroulette.com/tex/62725/the-notation-in-various-engines that's old and relates to old bugs isn't it? > > > > Doug McKenna > > > David
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