Since its merge Backpack has been long lacking in the documentation department. In particular, there are several questions of the implementation that are currently unaddressed in the codebase:

• What is the motivation for and semantics of the .bkp file format?
• How do Cabal (and other build systems) interact with
• Where are the Notes that do discuss Backpack found?
• How does Backpack interact with the EPS? How are hole instantiations incorporated into UnitIds?
• What shortcomings does the current implementation suffer from? For instance, until very recently (#17188) -j was not supported under Backpack. There are also known limitations regarding promotion (#13149). Do we have a comprehensive list of such limitations somewhere (perhaps in the user documentation)?

Furthermore, the users guide has not a single mention of the feature, its motivation, or user-facing interface.