A more thorough explanation:

Ope exceptionis is a Latin term that means "by force of exception." In legal terms, it refers to a plea made in a civil case that asserts a peremptory exception, claiming that the document on which the action is based is void.

An example of ope exceptionis would be a defendant in a breach of contract case claiming that the contract in question is void due to a lack of consideration. The defendant would argue that because there was no exchange of value between the parties, the contract is not legally binding and therefore cannot be the basis for the plaintiff's claim.

Another example would be a defendant in a property dispute case claiming that the deed to the property is void due to a defect in the chain of title. The defendant would argue that because the property was not properly transferred from the previous owner, the current owner does not have legal title to the property and therefore cannot bring a claim against the defendant.

These examples illustrate how a plea of ope exceptionis can be used to challenge the validity of a document on which a legal claim is based. By asserting that the document is void, the defendant can attempt to have the case dismissed or the claim against them invalidated.