What is the past perfect progressive?

Related questions

1. What are the 3 progressive tenses?
2. When Use present perfect progressive?
3. What is a progressive perfect verb?
4. When can I use present perfect?
5. Which helping verb is used in future perfect tense?
6. What does the present perfect tense express?
7. What is the formula for present perfect continuous tense?
8. What is perfect progressive aspect?
9. What is the structure of present indefinite tense?
10. When should we use present perfect tense?

Tags

1. #constructed
2. #tense
3. #continued
4. #until
5. #another
6. #participle
7. #continuous
8. #using
9. #known
10. #shows
11. #present
12. #perfect
13. #progressive
14. #started
15. #action