When writing the headnotes, the West editor gives each one a headline (broad topic) selected from a list of about 450 possibilities.
Some examples are Landlord and Tenant, Intoxicating Liquors, and Automobiles.
Finally, the editor will assign the headnote a specific subtopic, such as Injury to Tenant or Occupant. In West digests, this subtopic is represented by a number called a key number.
154 Insurance