# `policy.binding_invalid`

Policy names something that can't say who.

Area 9, [Policy](../topics/policy.md); not declinable; the next step is usually the agent's.

A field names who may do something only when it points at the caller, a reference to the principal's user entity; the same rule covers a membership's `scope:`, `member:` and `role:`, `tenant:`, and the lines under `actions:`:

```jadpo
type Handle = Text {
    max_length: 40
}

entity User {
    id: Uuid
    handle: Handle {
        unique: true
    }
}

principal {
    user: {
        subject: User.handle
    }
}

entity Note {
    id: Uuid
    owner_id: Uuid

    policy: {
        read: [owner_id]
    }
}
```

```text
error: `owner_id` doesn't point at a caller
 --> main.jadpo:23:16
   |
23 |         read: [owner_id]
   |                ^^^^^^^^ not a user field
  reason: A field names who may do this when it points at the caller: a reference to `User`, the principal's user entity (area 8), typed `User.id`. `Note.owner_id` isn't.
  next: Name a reference to the user, a membership role, or `Access` (agent)
  rule: policy.binding_invalid
  help: https://jadpo.dev/docs/errors/policy.binding_invalid

check failed: 1 error, 1 file
```