#17 more details on diff flex/JFlex

[Gerwin Klein]

in flex special characters lose their "special" meaning
inside a character class, with special-case syntax for
including square brackets themselves:
flex: [][]
JFlex: [\]\[]
Note also that [] and [^] are illegal in flex. Also,
["] vs. [\"] and I'm guessing the backslash itself (not
tested).

(reported by Dimitri Maziuk)