Major Description
The grammar uses a similar specification for LETTERs as the old Java-grammar. By intention most UTF-8 characters should possible to use for names to enable localization in languages using non-latin characters. This is especially important for DSLs.
Ast-transformations will take place after the Lexer. With the Lexer accepting his characters, ast-transformations are now able to handle more things like creating custom operators and so on.
This is a problem only for ANTLR 2.
ANTLR 4 is only missing the '#'-sign.
This maybe introduces a breaking change, because GStrings like "$first#$second" worked in the past, and now will not anymore. Before this change, "$first#" is interpreted as the value of the variable first plus a '#' sign. Now it is interpreted as the value of the variable first#.
This, of cause, is a problem for all newly added letters.