How do you know which HTML version I am using?

Related questions

1. What is doctype is it necessary to use in html5?
2. What is doctype in XML?
3. What is SGML and DTD?
4. What does doctype mean?
5. What is the html5 stack?
6. Is HTML 5 case sensitive?
7. Is doctype case sensitive?
8. How can we create doctype in html5?
9. What is doctype >? Is it necessary to use in html5?
10. Does html5 support offline storage?

Tags

1. #similar
2. #simply
3. #version
4. #application
5. #should
6. #other
7. #html5
8. #website
9. #doctype
10. #first
11. #interested
12. #looks
13. #something
14. #check
15. #normally
16. #source
17. #declaration