improve plugin docu

packages/overlayscrollbars/src/initialization.ts

@@ -86,7 +86,7 @@ export type Initialization = {
 };
 
 /** The initialization target element. */
-export type InitializationTargetElement = HTMLElement | HTMLTextAreaElement;
+export type InitializationTargetElement = HTMLElement; // | HTMLTextAreaElement;
 
 /**
  * The initialization target object.

packages/overlayscrollbars/src/plugins/plugins.ts

@@ -1,9 +1,19 @@
 import { each, isArray, keys, push } from '~/support';
 import type { OverlayScrollbars, OverlayScrollbarsStatic } from '~/overlayscrollbars';
 
+/** Describes the instance of a OverlayScrollbars plugin. */
 export type PluginInstance =
+  /** A `static` plugin. Its neither bound to a instance nor to the static object. */
   | Record<string, unknown>
+  /**
+   * A plugin which is bound to either a instance or to the static object.
+   * The function will be called multiple times. Once with the static object and each time a new instance is created.
+   * The plugin then can add new methods or fields to thow objects.
+   * These plugins should be side-effect free and deterministic. (same input produces same output)
+   */
   | ((staticObj?: OverlayScrollbarsStatic, instanceObj?: OverlayScrollbars) => void);
+
+/** Describes a OverlayScrollbars plugin. */
 export type Plugin<T extends PluginInstance = PluginInstance> = {
   [pluginName: string]: T;
 };