I recently read a thread related to a topic on Expat registration cards being reviewed? Part of that discussion was about what a Yellow book was or was not. Unfortunately, I cannot locate this site again after one day. Help!

1. What is a yellow book?
2. What are the requirements? Eligibility?
3. What Thai offices do you go to for this book?
4. Is it worthwhile to do?
5. Does it cost anything?
6. Is there a time requirement? Years in Thailand? Married to a Thai # of years?
7. If you have a Retirement O visa, what if anything does a Yellow Book enhance?

Appreciate any information on this subject. Please elaborate and add sites I can visit for further information in English.