Undo and redo doesn't work

[lifthrasiir]

In fact, it seems that it was intentionally disabled for no obvious reason.

[keepworking]

Yes, I have a lot of worries to support Undo and Redo.

document.exeCommand is deprecated, so I tried to create a corresponding function myself.

But that function rather broke the document when I did Undo and Redo.

I wanted to solve this part, so I thought hard about it, but I decided to deactivate it for now and implement it separately.