<field-of-search>
  <classification-national country="US"><text>435234</text></classification-national>
</field-of-search>

technical-data/field-of-search

Field of search indicates the classes/subclasses the examiner searched when examining the patent.

Element	INID	Description (delivered unformatted, either as single items or as ranges, as received from the USPTO)
classification-ipc	58	IPC Classes
classifications-ipcr	58	IPCR Classes
classification-national	58	US Classes
classifications-cpc		CPC Classes
classification-locarno		Locarno Classes

technical-data field-of-search