Improve documentation on webgl and View

src/ol/webgl/Buffer.js

@@ -4,20 +4,27 @@
 import {STATIC_DRAW, STREAM_DRAW, DYNAMIC_DRAW} from '../webgl.js';
 
 /**
+ * Used to describe the intended usage for the data: `STATIC_DRAW`, `STREAM_DRAW`
+ * or `DYNAMIC_DRAW`.
  * @enum {number}
  */
-const BufferUsage = {
+export const BufferUsage = {
   STATIC_DRAW: STATIC_DRAW,
   STREAM_DRAW: STREAM_DRAW,
   DYNAMIC_DRAW: DYNAMIC_DRAW
 };
 
-
+/**
+ * @classdesc
+ * Object used to store an array of data as well as usage information for that data.
+ * See the documentation of [WebGLRenderingContext.bufferData](https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/bufferData) for more info.
+ * @api
+ */
 class WebGLArrayBuffer {
 
   /**
    * @param {Array<number>=} opt_arr Array.
-   * @param {number=} opt_usage Usage.
+   * @param {number=} opt_usage Usage, either `STATIC_DRAW`, `STREAM_DRAW` or `DYNAMIC_DRAW`. Default is `DYNAMIC_DRAW`.
    */
   constructor(opt_arr, opt_usage) {