What is doctype is it necessary to use in html5?

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5. What is doctype and what happens if doctype is not declared in a document?
6. What is SGML and DTD?
7. What is doctype >? Is it necessary to use in html5?
8. What is doctype in XML?
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Tags

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