[mkgmap-dev] output of splitter isn't recognized by JOSM

Hi, does anybody know why the output of splitter is not recognized by JOSM? Is there a way to make splitter produce outputs that are compatible to normal .osm files like the ones downloaded by geofabrik? I would really like to use splitter to cut a country into managable chunks for offline editing in JOSM. Or wouldn't this work of other reasons I don't know yet? Thanks, Stefan