A collaborative authoring application provides an authoring environment in which two or more users can edit a document concurrently. Each user edits a copy of the document, sends updates to a master copy of the document, and receives updates from the master copy of the document. The authoring environment generally inhibits the users from providing conflicting editing instructions to the master copy of the document. For example, each user can generate a content lock about one or more data units within the document. The authoring environment may synchronize content locks automatically and content only at the request of the user.