@Override
		public void exitEveryRule(ParserRuleContext ctx) {
			System.out.println("exit    "+getRuleNames()[ctx.getRuleIndex()]+
							   ", LT(1)="+_input.LT(1).getText());
		}
This is all the parsing support code essentially; most of it is error recovery stuff.
runtime/Java/src/org/antlr/v4/runtime/Parser.java