Salve in nomine Domini!

Does anyone know whether the old rubric for vesting for Holy Mass, wherein the Priest is required to wear BOTH the dalmatic and Chausable, together with the subdeacon's Tunicle, is still in force for the celebration of the Extraordinary Form of the Mass??

I saw the Holy Father wearing all of the above for his Advent Masses in the Ordinary Form, but saw the OFM recently wearing just the Chausable and no Dalmatic underneath...... So what's the rule....????

Thanks....