How do XML files work?

Related questions

1. What is an XML schema file?
2. What is the alternative for XML and what are its advantages over XML?
3. Can XML tags have spaces?
4. What is whitespace in XML?
5. What is XML schema used for?
6. Does XML care about whitespace?
7. What is indent XML?
8. Where XML is used in applications?
9. What are XML files used for?
10. What is XML and use of XML?

Tags

1. #anything
2. #structure
3. #markup
4. #based
5. #language
6. #extension
7. #files
8. #transportation
9. #describe
10. #except
11. #storage
12. #themselves
13. #plain
14. #example
15. #extensible
16. #common