public String getDefaultActionScope() {
        switch ( getType() ) {
            case ANTLRParser.LEXER :
                return "lexer";
            case ANTLRParser.PARSER :
            case ANTLRParser.COMBINED :
                return "parser";
        }
        return null;
    }
Given a grammar type, what should be the default action scope?
 If I say @members in a COMBINED grammar, for example, the
 default scope should be "parser".
tool/src/org/antlr/v4/tool/Grammar.java