XML: A Two-part promise for the WWW
 
  - XML promised to deliver a markup language for the WWW which would mean
that 
   
    - You could design and/or choose your own vocabulary;
- You could mix vocabularies without confusion.
 
- Beyond the language (including XML Namespaces), two obligations followed
from that promise 
   
    - An approach to rendering so you could see your
documents;
- An approach to document structure definition so you could
control your documents.
 
- First CSS, then XSLT discharged the first obligation.
- XML Schema will discharge the second.