docs: add docs for RO interface

src/ResizeObserver.ts

@@ -4,6 +4,9 @@ import { ResizeObserverOptions } from './ResizeObserverOptions';
 import { isElement } from './utils/element';
 
 /**
+ * The ResizeObserver API is an interface for observing changes to Element’s size.
+ * It is an Element's counterpart to window.resize event.
+ * 
  * https://drafts.csswg.org/resize-observer-1/#resize-observer-interface
  */
 class ResizeObserver {
@@ -18,6 +21,13 @@ class ResizeObserver {
     ResizeObserverController.connect(this, callback);
   }
 
+  /**
+   * Observes an element,
+   * notifying the handler of the current and subsequent sizes.
+   * @param target Element to observe
+   * @param options Options to pass to the observer
+   * @returns {void}
+   */
   public observe (target: Element, options?: ResizeObserverOptions): void {
     if (arguments.length === 0) {
       throw new TypeError(`Failed to execute 'observe' on 'ResizeObserver': 1 argument required, but only 0 present.`)
@@ -28,6 +38,11 @@ class ResizeObserver {
     ResizeObserverController.observe(this, target, options);
   }
 
+  /**
+   * Stops observing the element for any further changes.
+   * @param target Element to stop observing
+   * @returns {void}
+   */
   public unobserve (target: Element): void {
     if (arguments.length === 0) {
       throw new TypeError(`Failed to execute 'unobserve' on 'ResizeObserver': 1 argument required, but only 0 present.`)
@@ -38,10 +53,17 @@ class ResizeObserver {
     ResizeObserverController.unobserve(this, target);
   }
 
+  /**
+   * Disconnects all observed targets.
+   * @returns {void}
+   */
   public disconnect (): void {
     ResizeObserverController.disconnect(this);
   }
 
+  /**
+   * @override
+   */
   public static toString (): string {
     return 'function ResizeObserver () { [polyfill code] }';
   }