docs: center of viewport example

README.md

@@ -151,7 +151,7 @@ Provide these as the options argument in the `useInView` hook or as props on the
 | Name                   | Type                      | Default     | Description                                                                                                                                                                                                                                                                                     |
 |------------------------|---------------------------|-------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | **root**               | `Element`                 | `document`  | The Intersection Observer interface's read-only root property identifies the Element or Document whose bounds are treated as the bounding box of the viewport for the element which is the observer's target. If the root is `null`, then the bounds of the actual document viewport are used.  |
-| **rootMargin**         | `string`                  | `'0px'`     | Margin around the root. Can have values similar to the CSS margin property, e.g. `"10px 20px 30px 40px"` (top, right, bottom, left).                                                                                                                                                            |
+| **rootMargin**         | `string`                  | `'0px'`     | Margin around the root. Can have values similar to the CSS margin property, e.g. `"10px 20px 30px 40px"` (top, right, bottom, left). Also supports percentages, to check if an element intersects with the center of the viewport for example "-50% 0% -50% 0%".                                |
 | **threshold**          | `number` or `number[]`    | `0`         | Number between `0` and `1` indicating the percentage that should be visible before triggering. Can also be an array of numbers, to create multiple trigger points.                                                                                                                              |
 | **onChange**           | `(inView, entry) => void` | `undefined` | Call this function whenever the in view state changes. It will receive the `inView` boolean, alongside the current `IntersectionObserverEntry`.                                                                                                                                                 |
 | **trackVisibility** 🧪 | `boolean`                 | `false`     | A boolean indicating whether this Intersection Observer will track visibility changes on the target.                                                                                                                                                                                            |