Oregon Revised Statutes Property Rights and Transactions § 105.015

The defendant shall not be allowed to give in evidence any estate, license or right of possession in the property in the defendant or another, unless the same is pleaded in the answer. If pleaded, the nature and duration of the estate, license or right of possession shall be set forth with the certainty and particularity required in a complaint. If the defendant does not defend for the whole of the property, the defendant shall specify for what particular part the defendant does defend.