10:		the key is in the generated source.
20:		enter a non-integer into form field and submit. the key is in the resulting
		traceback.
30:		change the value in the GET request to a non-integer. the key is in the
		resulting traceback.
40:		change the value in the POST request to a non-integer. the key is in the
		resulting traceback.
50:		change the quantity value (hidden form field) to something greater than the
		stated quantity limit. the key is in the resulting traceback. entering non-
		integers is caught and handled, so that no longer works.