'Search this document and, if nothing is found, the document directly
associated with its nearest zone, returning the first zone nav HTML
found.'

def get_zone_subnav_html(self):

    src = self.get_zone_subnav_local_html()
    if ((not src) and self.nearest_zone):
        src = self.nearest_zone.document.get_zone_subnav_local_html()
    return src
