Document internal props

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Features
 
+- Error [`props`](README.md#%EF%B8%8F-error-properties) now preserve
+  [property descriptors](https://github.com/ehmicky/redefine-property)
+- Error [`props`](README.md#%EF%B8%8F-error-properties) can be marked as
+  [non-enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties)
+  by [prefixing their name](README.md#internal-error-properties) with `_`
 - [`plugin.properties()`](docs/plugins.md#properties) can now also return
   non-enumerable properties by prefixing their name with `_`
 

README.md

@@ -198,6 +198,25 @@ const error = new InputError('...', { props: { isUserError: true } })
 console.log(error.isUserError) // true
 ```
 
+### Internal error properties
+
+Error properties that are internal or secret can be prefixed with `_`. This
+makes them
+[non-enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties),
+which prevents iterating or logging them.
+
+<!-- eslint-disable no-underscore-dangle -->
+
+```js
+const error = new InputError('...', {
+  props: { userId: 6, _isUserError: true },
+})
+console.log(error.userId) // 6
+console.log(error._isUserError) // true
+console.log(Object.keys(error)) // ['userId']
+console.log(error) // `userId` is logged, but not `_isUserError`
+```
+
 ## 🎀 Wrap errors
 
 ### Throw errors

docs/plugins.md

@@ -118,9 +118,10 @@ _Type_: `(info) => object`
 Set properties on `error.*` (including `message` or `stack`). The properties to
 set must be returned as an object.
 
-If a property's name starts with `_`, it is marked as
+Error properties that are internal or secret can be prefixed with `_`. This
+makes them
 [non-enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties),
-i.e. it can neither be iterated nor logged.
+which prevents iterating or logging them.
 
 ```js
 export default {

types/plugins/shape.d.ts

@@ -178,6 +178,11 @@ export interface Plugin {
    * Set properties on `error.*` (including `message` or `stack`).
    * The properties to set must be returned as an object.
    *
+   * Error properties that are internal or secret can be prefixed with `_`.
+   * This makes them
+   * [non-enumerable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties),
+   * which prevents iterating or logging them.
+   *
    * @example
    * ```js
    * export default {