code: def _verify(self, path_prefix=None):
          
          for field, spec in self.doc_spec.iteritems():
              path = self._append_path(path_prefix, field)
  
              # Standard dict-based spec
              if isinstance(spec, dict):
                  self._verify_field_spec(spec, path)
              else:
                  raise SchemaFormatException("Invalid field definition for {}", path)
docs: Verifies that this schema's doc spec is valid and makes sense.