Row size limits in Mysql w.r.t to TEXT and BLOB columns

There is a well-known limitation in Mysql for row size which 65,535 bytes. While going through the docs , I have found that > BLOB and TEXT columns only contribute 9 to 12 bytes toward the row > size limit because their contents are stored separately from the rest > of the row. I did go through the MySQL documentation but unable to understand when a TEXT column will contribute 9 bytes and when it will contribute 12 bytes. Can anyone explain how to interpret the statement?