Update README.md

Co-authored-by: Timothy Gu <timothygu99@gmail.com>

Author: ExE-Boss

README.md

@@ -18,30 +18,33 @@ This package exposes two flavors of the `CSSStyleDeclaration` interface dependin
 
 ### `cssstyle` module
 
-This module default-exports the `CSSStyleDeclaration` interface constructor, with the change that it can be constructed and takes an `onChangeCallback` optional parameter:
-
-```ts
-export = class CSSStyleDeclaration {
-  /**
-   * @param onChangeCallback The callback that is invoked whenever a property changes.
-   */
-  constructor(onChangeCallback?: ((cssText: string) => void) | null);
+This module default-exports the `CSSStyleDeclaration` interface constructor, with the change that it can be constructed with an optional `onChangeCallback` parameter. Whenever any CSS property is modified through an instance of this class, the callback (if provided) will be called with a string that represents all CSS properties of this element, serialized. This allows the embedding environment to properly reflect the style changes to an element's `style` attribute.
+
+Here is a crude example of using the `onChangeCallback` to implement the `style` property of `HTMLElement`:
+```js
+const CSSStyleDeclaration = require('cssstyle');
+
+class HTMLElement extends Element {
+  constructor() {
+    this._style = new CSSStyleDeclaration(newCSSText => {
+      this.setAttributeNS(null, "style", newCSSText);
+    });
+  }
+
+  get style() {
+    return this._style;
+  }
+
+  set style(text) {
+    this._style.cssText = text;
+  }
 }
 ```
 
 ### `cssstyle/webidl2js-wrapper` module
 
-This module exports the `CSSStyleDeclaration` [interface wrapper API](https://github.com/jsdom/webidl2js#for-interfaces) generated by [webidl2js](https://github.com/jsdom/webidl2js).
+This module exports the `CSSStyleDeclaration` [interface wrapper API](https://github.com/jsdom/webidl2js#for-interfaces) generated by [webidl2js](https://github.com/jsdom/webidl2js). Unlike the default export, `CSSStyleDeclaration` constructors installed by the webidl2js wrapper do _not_ support construction, just like how they actually are in browsers. Creating new `CSSStyleDeclaration` objects can be done with the [`create`](https://github.com/jsdom/webidl2js#createglobalobject-constructorargs-privatedata) method of the wrapper.
 
 #### `privateData`
 
-The `privateData` argument takes the following properties:
-
-```ts
-interface CSSStyleDeclarationPrivateData {
-  /**
-   * The callback that is invoked whenever a property changes.
-   */
-  onChangeCallback?: ((cssText: string) => void) | null
-}
-```
+The `privateData` parameter of `create` and `createImpl` provides a way to specify the `onChangeCallback` that is a constructor parameter in the default export. Only the `onChangeCallback` property is supported on `privateData` currently, with the same semantics as the constructor parameter documented above.