rem: get icalString() { throw Components.results.NS_NOT_IMPLEMENTED; 
add: get previous() { if (this.item.recurrenceInfo) return this.item.recurrenceInfo.getPreviousOccurrence(this.item, aStartDate); return null; 
context:     get icalString() {        throw Components.results.NS_NOT_IMPLEMENTED;    },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/91536ce225393e0f700a443aabe5c12856c92fef/calItemBase.js/clean/calendar/base/src/calItemBase.js