A more thorough explanation:

haec est conventio

haec est conventio is a Latin phrase that means "this is the agreement." It was commonly used in written agreements in the past.

Example 1: John and Jane signed a contract for the sale of a car. The contract began with the words "haec est conventio," indicating that the document was a formal agreement between the two parties.

Example 2: In a medieval land deed, the phrase "haec est conventio" was used to indicate that the document was a binding agreement between the landowner and the tenant.

The examples illustrate how "haec est conventio" was used to indicate that a written document was a formal agreement between two parties. The phrase was commonly used in legal documents in the past.