If they have a browser that supports HTML, they can view any Office 2000 file. HTML provides the viewing framework while XML provides the framework for data stored within that HTML document. Within the Office 2000 document is a namespace tag that identifies the schema. When a browser or other program that can display HTML sees the Office 2000 document, it uses the schema and its associated style information to first process and then display the document. When Office200 applications open a document, they use the schema to access the underlying XML data structure.
Some schemas are private, while other others are publicly published.