add comment about react >= 17 focus event listeners

Author: adri1wald

packages/slate-react/src/components/slate.tsx

@@ -72,6 +72,9 @@ export const Slate = (props: {
   useIsomorphicLayoutEffect(() => {
     const fn = () => setIsFocused(ReactEditor.isFocused(editor))
     if (IS_REACT_VERSION_17_OR_ABOVE) {
+      // In React >= 17 onFocus and onBlur listen to the focusin and focusout events during the bubbling phase.
+      // Therefore in order for <Editable />'s handlers to run first, which is necessary for ReactEditor.isFocused(editor)
+      // to return the correct value, we have to listen to the focusin and focusout events without useCapture here.
       document.addEventListener('focusin', fn)
       document.addEventListener('focusout', fn)
       return () => {