public GrammarAST expandParameterizedLoop(GrammarAST t) {
        // todo: update grammar, alter AST
        return t;
    }
Find and replace
     ID*[','] with ID (',' ID)*
     ID+[','] with ID (',' ID)+
     (x {action} y)+[','] with x {action} y (',' x {action} y)+

 Parameter must be a token.
 todo: do we want?
tool/src/org/antlr/v4/tool/GrammarTransformPipeline.java