``` `margin` and `threshold` allow control over exactly when the loading is triggered as the element comes into view. `margin` can reduce or extend the detection area of the container and `threshold` can determine what proportion of the image needs to be within the area. Demo is based on [this example of intersection-observer](https://github.com/wilsonpage/in-sixty/blob/gh-pages/intersection-observer/index.html) If used on a browser without support for `IntersectionObserver` a polyfill will be loaded automatically from the [polyfill.io service](https://polyfill.io/v2/docs/). Configure this with the following code in `index.html`: ``` ```