Ok. The code repository has experimental code for case insensitivity. The way it works is: You use your existing lex file and use the /codeinsensitive command line flag, or option inside the source.
GPLEX constructs an automaton that is case insensitive. However yytext contains the actual untransformed characters that were read from input.
What are the drawbacks? Case insensitivity is an incomputable problem at its heart, given that for some languages a single character in one case transforms into two or more characters in the alternative case, or has different choices depending on where
the character is in the word. The current rule that GPLEX uses is the that notion of ToUpper and ToLower are defined by the culture setting of the MACHINE ON WHICH GPLEX RUNS. This may not be the same as the culture setting on the machine on which
the generated scanner runs.
However, if you want to create a scanner for an ASCII character set or simple cases of Latin languages then it should work fine.
As usual, post any bugs to the issues tab.