code: def _tostring(value):
          '''Convert value to XML compatible string'''
          if value is True:
              value = 'true'
          elif value is False:
              value = 'false'
          elif value is None:
              value = ''
          return unicode(valuef _tostring(value):
          '''Convert value to XML compatible string'''
          if value is True:
              value = 'true'
          elif value is False:
              value = 'false'
          elif value is None:
              value = ''
          return unicode(value)
docs: Convert value to XML compatible string