void checkNumPrequels(List<GrammarAST> options,
						  List<GrammarAST> imports,
						  List<GrammarAST> tokens)
	{
		List<Token> secondOptionTokens = new ArrayList<Token>();
		if ( options!=null && options.size()>1 ) {
			secondOptionTokens.add(options.get(1).token);
		}
		if ( imports!=null && imports.size()>1 ) {
			secondOptionTokens.add(imports.get(1).token);
		}
		if ( tokens!=null && tokens.size()>1 ) {
			secondOptionTokens.add(tokens.get(1).token);
		}
		for (Token t : secondOptionTokens) {
			String fileName = t.getInputStream().getSourceName();
			g.tool.errMgr.grammarError(ErrorType.REPEATED_PREQUEL,
									   fileName, t);
		}
	}
Value of caseInsensitive option (false if not defined)
tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java