- Enhancement: Return a Promise for Editor's setCustomHandlers,

`loadFromString`, `loadFromDataURI` so known when ready and set
- Docs (Refactoring): Formally specify `Promise` resolve type;
    add `typedef` for dialog result object; add an
    `ArbitraryCallbackResult` type

test/ui-tests/accessibility.js

@@ -3,12 +3,15 @@
 // https://github.com/helen-dikareva/axe-testcafe
 import axeCheck from 'axe-testcafe';
 
+/**
+* @external AxeResult
+*/
 /**
  * @external TestcafeTest
 */
 /**
  * @param {external.TestcafeTest} t
- * @returns {Promise}
+ * @returns {Promise<external:AxeResult>}
  */
 function axeCheckWithConfig (t) {
   return axeCheck(