What is doctype >? Is it necessary to use in html5?

Related questions

1. How do you know which HTML version I am using?
2. Does html5 need doctype?
3. What is SGML and DTD?
4. What is doctype in XML?
5. What DTD means?
6. How can we create doctype in html5?
7. What is doctype is it necessary to use in html5?
8. What is the difference between HTML and html5?
9. Where is my website HTML?
10. How do I know html5?

Tags

1. #html5
2. #doctype
3. #against
4. #correctly
5. #ensure
6. #developed
7. #elements
8. #doctypes
9. #always
10. #existence
11. #means
12. #beginning
13. #browsers
14. #document
15. #render