A camera that submits like a file input
A device produces a Blob; a form expects a FileList, and FileList is read-only. The one constructible path, and what it saves you on the server.
A foreign key to any unique column
Two ways to point at a row of another form — by id, or by any UNIQUE column. Why the second exists, and what building SQL against runtime tables costs.
Sixteen operators, six actions, two implementations
Conditional form logic in the browser is presentation, not validation. Keeping show, enable and require independent — and the half that must exist twice.
A form that does not exist when Django starts
A form builder means the form does not exist at import time. Here is the dispatch, the degradation rule, and the N+1 that a dict literal hides.