You're building a real-time collaborative document editing application. Multiple users can edit the same document simultaneously, and changes made by one user should be reflected instantly for everyone else.

Question: Design a data structure and efficient algorithms to represent the document and handle concurrent edits. The data structure should be efficient for insertions, deletions, and character updates at any position in the document. Additionally, consider how to handle concurrency issues like race conditions and ensure data consistency when multiple users modify the document simultaneously.