How many types of DTD are there in XML?

Related questions

1. What is DTD in XML?
2. What is XML document validation?
3. What is use of DTD in XML?
4. What is internal DTD in XML?
5. Why do we need DTD in XML?
6. Why do we need XML parser?
7. What is a DTD file in XML?
8. What is XML mapping?
9. What is the difference between HTML and XML?
10. What is XML schema validation?

Tags

1. #attributes
2. #elements
3. #private
4. #included
5. #standalone
6. #public
7. #referenced
8. #defined
9. #there
10. #entities
11. #document
12. #external
13. #types
14. #rules
15. #declaration