code: def apply(self, root):
          
          if not self.filter.match(root, self.ns):
              return
          if self.exists(root):
              return
          node = Element('import', ns=self.xsdns)
          node.set('namespace', self.ns)
          if self.location is not None:
              node.set('schemaLocation', self.location)
          log.debug('inserting: %s', node)
          root.insert(node)
docs: Apply the import (rule) to the specified schema.
          If the schema does not already contain an import for the
          I{namespace} specified here, it is added.
          @param root: A schema root.
          @type root: L{Element}