W3C: XML design principles

Draft DD-1996-0001 - Design Principles for XML
  1. XML shall be straightforwardly usable over the Internet.
  2. XML shall support a wide variety of applications.
  3. XML shall be compatible with SGML.
  4. It shall be easy to write programs which process XML documents.
  5. The number of optional features in XML is to be kept to the absolute minimum
  6. XML documents should be human-legible and reasonably clear.
  7. The XML design should be prepared quickly.
  8. The design of XML shall be formal and concise.
  9. XML documents shall be easy to create.
  10. Terseness is of minimal importance.