Worked on AvaloniaUI/AvaloniaEdit, focusing on improving the maintainability and internal consistency of the TextDocument component. Addressed API hygiene by enhancing encapsulation, specifically by changing the visibility of the _undoStack field from public to private. This adjustment reduced the risk of unintended external mutations and established clearer boundaries for future development. The work leveraged C# and object-oriented programming principles to strengthen software design, making the codebase more robust and easier to refactor. No major bug fixes were addressed during this period, but the targeted feature delivered business value by supporting safer maintenance and providing clear commit-level documentation for traceability.