About the ext folder:
From my post: http://reboot.pro/in...445#entry217826
I'm going to answer myself, the ext folder contains a set of the previously called grubutils (external utilities that can be run from grub4dos).
On this page on RMPrepUSB site by our fellow steve6375, I found a brief description and info of their use, at least for the MBR version of grub4dos.
The page also includes interesting info to make use of this utilities on the creation of Batch files for grub4dos (MBR version).
NOTE: It seems the linked page on RMPrepUSB is not very recent and some info could be outdated.
It would be good if some of our chinese friends, that come frecuently to this forum, and have more knowledge of the recent developments in grub4dos for MBR and also for UEFI could give us a more complete and updated info.