# The error `magnet.no-part`

**user**: the script can change it: the error says what happened in the experiment's names, and what to write instead.

**On the refusal list: no test names this code**, since no file under `tests/` names it. A test may still raise it without naming it, and none asserts it: what its message and action say is read from the source below. The hook that records which codes a test raises has not landed, so until it does the list says names and never raises. The list (`docs/ratchets/refusal_codes.txt`) only shrinks.

Where MIME gives it, with what its message says happened and what its action says to do (`{…}` is filled in from the experiment):

- in `mime/build/_plan.py`:
  - what happened: `body {…} declares parts, and its magnet {…} is not among them: its moment is derived from its parts`
  - what to do: `declare the magnet's part: parts={{…}: Part(...)}`

Reading an error and reaching its full traceback: [reading an error](../reading_errors.md). Every code: [the index](index.md).