@Override
	public void discoverRule(RuleAST rule, GrammarAST ID,
							 List<GrammarAST> modifiers,
							 ActionAST arg, ActionAST returns,
							 GrammarAST thrws, GrammarAST options,
							 ActionAST locals,
							 List<GrammarAST> actions, GrammarAST block)
	{
		// TODO: chk that all or no alts have "# label"
		checkInvalidRuleDef(ID.token);
	}
Value of caseInsensitive option (false if not defined)
tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java