spanish 21 with redouble

will be traveling to a location where they offer spanish 21 h17 and redouble option. As I understand, after doubling, you can double again and get another card.

I looked up basic strategy from Wizard of Odds.com.
Most of it is pretty obvious, but I am having trouble understanding or believing correctness for his page "player has already doubled".
If I am reading correct, player has 6 or 7, bs is to double against dealer 3-6 and player 9 bs is redouble against any dealer card?
Any other references for bs with these rules.