add: if (this.readOnly) throw Components.interfaces.calIErrors.CAL_IS_READONLY; 
context:     modifyItem: function (aNewItem, aOldItem, aListener) {        if (aNewItem.calendar == null) {            // XXX Can't modify item with NULL parent            throw Components.results.NS_ERROR_FAILURE;        }        aNewItem.calendar.modifyItem (aNewItem, aOldItem, aListener);    },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/10aa71fd0bd91b8cabbafaa5c1a8ab2ea0f210dc/calCompositeCalendar.js/buggy/calendar/providers/composite/calCompositeCalendar.js