Denksleutel

Tony Ryan's thinking keys (denksleutels): short tasks that make a pupil
think differently, like "name eight things you would never find in a Roman
fort". There is no right answer: the pupil comes up with as many ideas as
they can, and the teacher judges them on fluency, flexibility and
originality. Works for any subject: the content comes from the task.

Write the task itself in the task's `prompt`. The field adds two things:

- **In the booklet**, a card with the key's number, its name and a
  one-line explanation (`uitleg: false` leaves the explanation out), plus
  what the key gives the pupil to think about.
- **On the answer sheet**, a form that fits the key.

| `sleutel` | Answer sheet | Needs |
| --- | --- | --- |
| `omgekeerd`, `wat-als`, `variaties`, `voorspelling`, `andere-gebruiken`, `belachelijk`, `brainstorm`, `alternatieven`, `interpretatie` | `aantal` numbered lines | |
| `overeenkomsten`, `gedwongen-verband` | `aantal` numbered lines | `dingen`: two things |
| `vragen` | `aantal` numbered lines | `antwoord`: the answer, printed big |
| `muur` | `aantal` numbered lines | `muur`: what seems impossible, printed on a brick wall |
| `plaatjes` | `aantal` numbered lines | a strange drawing of lines and a circle; `plaatje` picks another one |
| `nadelen` | `aantal` rows: disadvantage, and how to fix it | |
| `alfabet` | a line per letter, A to Z or `letters` | |
| `bar` | groter maken, iets toevoegen, iets vervangen, and a drawing box (`tekening: false` leaves it out) | |
| `combinatie` | the features of each thing, a drawing and an explanation | `dingen`: two things |
| `uitvinding` | a drawing and an explanation | |
| `bouw` | a drawing and an explanation | `materialen`: the only materials allowed |

`aantal` (3 to 12) defaults to 5 to 10 by key; more than 6 go in two
columns. A setting that doesn't belong to the key is an error, and so is a
key without what it needs.

`voorbeelden` are example answers for the teacher. They go into the model
answer and the answer key, never to the pupil: in list order, one per
letter for `alfabet` (matched by first letter), groter, toevoegen and
vervangen for `bar`, the explanation for the drawing keys. For `nadelen`
they are the disadvantages, with a matching solution per disadvantage in
`oplossingen`.

Not graded automatically: every area goes to the teacher.

```yaml
- type: task
  id: q5
  prompt: Noem acht dingen die je **nooit** in een Romeins fort zou vinden.
  answer:
    type: tim/denksleutels@1.0.0
    sleutel: omgekeerd
    voorbeelden: [Een stopcontact, Een trampoline]
```