This is a Vim plugin that visualizes the undo history of a buffer as a tree, allowing users to navigate between different undo branches. It parses Vim's internal `undotree()` data structure and renders an ASCII representation in a dedicated split window. The architecture follows an object-oriented pattern in Vim script, with classes for panels (undotree and diffpanel) encapsulating state and behavior. Key features include: window layout customization, diff panel with sign highlighting, relative timestamps, configurable tree shapes, and support for persistent undo. The plugin is purely Vim script and depends only on an external diff command for the diff panel. It is well-maintained, actively used, and avoids deprecated Vim APIs. The code demonstrates high craftsmanship in Vim scripting, particularly in the ASCII tree rendering algorithm and the diff caching mechanism.