Bugzilla mapping with Checkbox Multi-Select List

I am trying to use the Bugzilla Bug Report method to import work items. The default mapping does not support the Bugzilla "flags" feature but I am trying to map it by writing some pre-processed code. However, there is no documentation showing how the XML for a Checkbox Multi-Select List looks in RTC's work item would map for me to write the correct xml conversion. If I can see what the XML the mapping tool is expecting to map to a Checkbox Multi-Select List the I can create the xml to match. What would that look like, for example, for a type "flags" with multi-select string values of "x", "y", and "z"?