How is XML related to HTML?

Related questions

1. What is .xml used for?
2. For what XML is used?
3. What is Whatwg URL?
4. What is the need of XML?
5. What is doctype used for?
6. What is the purpose of the doctype command?
7. How is HTML different from XML?
8. What is XML and why do we use it?
9. What is the advantage of XML?

Tags

1. #other
2. #purpose
3. #while
4. #languages
5. #simple
6. #transfer
7. #parsing
8. #document
9. #standard
10. #language
11. #markup
12. #whereas
13. #related
14. #presentation
15. #define
16. #predefined
17. #where
18. #store