[docs] Documented setUseStrictIteration

Author: Michel Weststrate

website/docs/api.md

@@ -32,6 +32,7 @@ title: API overview
 | `produceWithPatches` | Works the same as `produce`, but instead of just returning the produced object, it returns a tuple, consisting of `[result, patches, inversePatches]`. | [Patches](./patches.mdx) |
 | `setAutoFreeze` | Enables / disables automatic freezing of the trees produces. By default enabled. | [Freezing](./freezing.mdx) |
 | `setUseStrictShallowCopy` | Can be used to enable strict shallow copy. If enable, immer copies non-enumerable properties as much as possible. | [Classes](./complex-objects.md) |
+| `setUseStrictIteration` | Controls iteration behavior: pass `false` for loose iteration (enumerable properties only, better performance) or `true` for strict iteration (includes symbols and non-enumerable properties). By default disabled (loose iteration). |  |
 
 ## Importing immer
 

website/docs/performance.mdx

@@ -9,8 +9,7 @@ title: Immer performance
 		data-ea-type="image"
 		className="horizontal bordered"
 	></div>
-</center>
-<details>
+</center> <details>
 	<summary className="egghead-summary">
 		egghead.io lesson 5: Leveraging Immer's structural sharing in React
 	</summary>
@@ -29,8 +28,7 @@ title: Immer performance
 	>
 		Hosted on egghead.io
 	</a>
-</details>
-<details>
+</details> <details>
 	<summary className="egghead-summary">
 		egghead.io lesson 7: Immer will try to re-cycle data if there was no
 		semantic change
@@ -80,6 +78,19 @@ enableArrayMethods()
 
 This plugin optimizes array operations like `filter`, `find`, `some`, `every`, and `slice` by avoiding proxy creation for every element during iteration. Without the plugin, iterating a 1000-element array creates 1000+ proxies. With the plugin, callbacks receive base values, and proxies are only created for elements you actually mutate.
 
+### Use loose iteration for better performance
+
+By default, Immer uses loose iteration which only processes enumerable string properties. This is faster than strict iteration which includes symbols and non-enumerable properties. For most use cases, the default is optimal:
+
+```javascript
+import {setUseStrictIteration} from "immer"
+
+// Default: false (loose iteration for better performance)
+setUseStrictIteration(false)
+```
+
+Only enable strict iteration if you specifically need to track symbol or non-enumerable properties.
+
 ### Pre-freeze data
 
 When adding a large data set to the state tree in an Immer producer (for example data received from a JSON endpoint), it is worth to call `freeze(json)` on the root of the data that is being added first. To _shallowly_ freeze it. This will allow Immer to add the new data to the tree faster, as it will avoid the need to _recursively_ scan and freeze the new data.