docs: def validate(self):
          """Validate process descriptor."""
          required_fields = ('slug', 'name', 'process_type', 'version')
          for field in required_fields:
              if getattr(self.metadata, field, None) is None:
                  raise ValidationError("process '{}' is missing required meta attribute: {}".format(
                      self.metadata.slug or '<unknown>', field))
  
          if not PROCESSOR_TYPE_RE.match(self.metadata.process_type):
              raise ValidationError("process '{}' has invalid type: {}".format(
                  self.metadata.slug, self.metadata.process_type))