The definition of list/@type suggests these values:
list items are numbered or lettered.
list items are marked with a bullet or other typographic device.
list items are not numbered or bulleted. [Default]
each list item glosses some term or concept, which is given by a label element preceding the list item.
However, the stylesheets are peppered with uses of "unordered" (which used to be in there, but is not any more). These should be replaced with "bulleted", presumably.