improve jsdoc comments

src/utils/Snapshot.js

@@ -10,17 +10,34 @@ export class Snapshot {
    * @param {DeleteSet} ds delete store
    * @param {Map<number,number>} sm state map
    * @param {Map<number,string>} userMap
+   * @private
    */
   constructor (ds, sm, userMap) {
+    /**
+     * @type {DeleteSet}
+     * @private
+     */
     this.ds = new DeleteSet()
+    /**
+     * State Map
+     * @type {Map<number,number>}
+     * @private
+     */
     this.sm = sm
+    /**
+     * @type {Map<number,string>}
+     * @private
+     */
     this.userMap = userMap
   }
 }
 
 /**
  * @param {AbstractItem} item
- * @param {Snapshot} [snapshot]
+ * @param {Snapshot|undefined} snapshot
+ *
+ * @protected
+ * @function
  */
 export const isVisible = (item, snapshot) => snapshot === undefined ? !item.deleted : (
   snapshot.sm.has(item.id.client) && (snapshot.sm.get(item.id.client) || 0) > item.id.clock && !isDeleted(snapshot.ds, item.id)