[bobbylarrybobby]

This was my first thought. A timeline is nice, but the problem with a linear undo history is that if you undo and then edit, you lose access to the state before you undid. A tree is clearly the right structure for undo history.

[wtetzner]

You could just append a new state to the end of the timeline when you “undo”, so you never lose history. This is how undo works in Emacs by default.

[Brian_K_White]

Heck it's how boring business apps handle bookkeeping data since forever. You never delete a record to correct a mistake, you create a new record to do it.

[b3n]

The tree structure is inherently flawed for storing undos when using features like undoing within a specific region, because the new state doesn't map to any previous node on the tree.

By default, Emacs has a linear undo structure, while still allowing you to never lose history.