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
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
