Over 10 years ago, the District of Delaware adopted its "Default Standard" for discovery, which sets forth several basic rules for discovery, particularly in patent actions.
One of the rules is the requirement to produce "core technical documents" early in the case:
Within 30 days after receipt of the [list of accused products and asserted patents], each defendant shall produce to the plaintiff the core technical documents related to the accused product(s), including but not limited to operation manuals, product literature, schematics, and specifications.
Pretty quickly after its adoption, the Court held that this includes non-public documents, after parties started trying to skirt the rule by dumping user manuals on the patentee.
These days, …