The subject of trade usages is at once ancient and fresh. It is ancient because the question of the legal characterization of usages is an old favorite of legal theorists, and makes appearances quite regularly at conferences. It is fresh because the practice of what has come to be known as transnational law has given a renewed role to usages, which I think forces is to address the concept more directly and candidly.
Fabien Gélinas, Toward a Transnational Law of Trade Usages?, 7 Y.B. Arb. & Mediation 49 (2015).