You may have a custom DTD, or need to use an industry standard DTD for your documents. However, you still need to provide your authors with a way to easily create and edit documents based on it.
x4o allows you to use any valid XML or SGML DTD*. By associating your DTD with x4o, you can customize the formatting, the application behaviors, the user interface, and even the deployment to end-users. You can allow XML authoring to be as constrained or loose, and as hidden or visible, as required. And all the while, your authors are still working in the familiar Microsoft Word environment.
* x4o can also be configured to support schemas.