unknown_local_form

Form head in a slot-local slot matches neither a local form nor any global form.

A slot may carry inline slot-local form definitions on either a keyword ((key :name shape :type form (form …) (form …))) or a form’s positional slot (inline (form …) children directly under the parent (form …)). A form value in that slot resolves local-first: the local forms shadow same-named globals, and a head that isn’t local still falls back to the global catalog (additive). Only when the head matches neither a local form nor any global form is this emitted, at the slot path: the key path for a keyword slot (e.g. [canvas shape]) or the parent form’s path for a positional slot (e.g. [canvas]), listing the allowed local heads. The generic unknown_form is suppressed for that node so you get one precise diagnostic, not two.

A qualified head (<plugin>/<form>) bypasses the locals entirely and resolves against the global catalog only, so a typo’d qualified head yields unknown_form, not this.

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Run sjon explain unknown_local_form to read this at a terminal, browse every code, or work through diagnostics-driven repair if you want the habit rather than the answer.