the lccode tables are set by the macro layer not the engine code, it reads in The Unicode consortium data file tex/generic/unicode-data/UnicodeData.txt and sets the lccode values and catcode values according to the data there.
see tex/generic/unicode-data/load-unicode-data.tex which is loaded at format creation tex/generic/tex-ini-files/xetex.ini David On Sun, 24 Nov 2019 at 02:12, Doug McKenna <d...@mathemaesthetics.com> wrote: > > When the LaTeX format is built, there are tests for whether or not a > Unicode-aware TeX engine is doing the work. I presume that XeTeX is such a > Unicode-aware engine, though I'm not familiar with what the definition of > "Unicode-aware TeX engine" actually is (separate issue). > > During the input of various hyphenation pattern files (a group for each > language code), the first such file that uses non-ASCII Unicode code points > is for Ancient Greek, in the file > > /usr/local/texlive/2017/texmf-dist/tex/generic/hyph-utf8/patterns/texhyph-grc.tex > > at line 61, which starts out > > α1 ε1 η1 ι1 ο1 υ1 ω1 ϊ1 ... > > TeX's code and specification says that only lowercase letters can appear in > pattern words, and the definition within TeX's source code of a lowercase > letter is any entry in the \lccode table that, when indexed by a character, > delivers itself. > > But as near as I can tell, during the building of the LaTeX format (i.e., > running "latex.ltx") there is no TeX source code that installs any of these > Greek letters into the \lccode table. Therefore, I'm concluding that the > XeTeX engine does this itself when it initializes, rather than awaiting any > TeX source code to do it. > > But there are a whole lot of lowercase letters in Unicode, so I'm wondering > how XeTeX determines legal lowercase letters for initial pattern files? > > I've tried looking at some version of the xetex.web code, but without > illumination, I'm afraid. > > TIA, > > Doug McKenna > > >
