Document code-input_load event

Author: WebCoder49

docs/interface/js/_index.md

@@ -6,6 +6,19 @@ title = '`code-input` vs the `textarea` in JavaScript'
 
 > Contributors: 2025 Oliver Geer
 
-Once registered, `code-input` elements support the JavaScript properties and events used with a `textarea` element, because they are built around them. Try swapping out your `textarea` element in your JavaScript application for a `code-input`! If it doesn't work, [submit a bug report](https://github.com/WebCoder49/code-input/issues).
+[Once registered](#code-input_load), `code-input` elements support the JavaScript properties and events used with a `textarea` element, because they are built around them. Try swapping out your `textarea` element in your JavaScript application for a `code-input`! If it doesn't work, [submit a bug report](https://github.com/WebCoder49/code-input/issues).
 
 If you want to replace a `textarea` with a `code-input` in an application that doesn't need JavaScript, [look here](../forms). We support HTML5 forms, and progressive enhancement so JavaScript isn't needed!
+
+## The `code-input_load` event {code-input_load}
+
+Each `code-input` element fires a `code-input_load` event when it, its template and its plugins have been fully registered. You should carry out initialisation code for `code-input` elements in a handler for this event:
+```javascript
+// TODO: Get code-input element as codeInputElement
+codeInputElement.addEventListener("code-input_load", () => {
+    // TODO: Initialisation code
+    // TODO: Add event handlers to the element here.
+});
+```
+
+For backwards compatibility, you should also implement the subset of the functionality that doesn't require `code-input.js` on the `<textarea data-code-input-fallback>` element before load, if you have one. For backwards compatibility and technical reasons, event handlers registered in HTML attributes like `onchange` of the textarea will be passed to the code-input element when it is registered, but event listeners registered like that above will not.