Viewing the DTDs
All of the Microsoft Help file formats are defined using XML. Each file has its own document type definition (DTD), which specifies the relationships between the tags and attributes that make up the file.
The DTD resources are stored in a compiled Help (.HxS) file that uses the namespace ms-help://hx. This file is installed and registered on your computer in one of two ways:
When you install Microsoft Help Workshop.
The first time you run HxComp.exe.
If you have taken one of the above steps, you can view the DTD files by clicking the links below. You can also save the DTDs to your local computer by right-clicking one of the links below and selecting Save Target As.