1) an expression that validates a Java identifier

2) clock time.     H:MM am|pm

	9:03 am		// legal
        12:30 pm	// legal
        3:40 am		// legal
	34:56 pm     // illegal
        9:61 pm	     // illegal

3) IP address

	A.B.C.D		// A,B,C,D are 0-255

	192.168.0.0     // legal
	255.255.255.255 // legal
	1.2.3.4		// legal
	256.34.45.56	// ILLEGAL