docs: def build(self, builder):
          """Build XML by appending to builder
          :Example:
          <StudyEventData StudyEventOID="SCREENING" StudyEventRepeatKey="1" TransactionType="Update">
  
          """
          params = dict(StudyEventOID=self.study_event_oid)
  
          if self.transaction_type is not None:
              params["TransactionType"] = self.transaction_type
  
          if self.study_event_repeat_key is not None:
              params["StudyEventRepeatKey"] = str(self.study_event_repeat_key)
  
          # mixins
          self.mixin()
          self.mixin_params(params)
  
          builder.start("StudyEventData", params)
  
          # Ask children
          for form in self.forms:
              form.build(builder)
  
          if self.signature is not None:
              self.signature.build(builder)
  
          for annotation in self.annotations:
              annotation.build(builder)
  
          builder.end("StudyEventData")