I am sad that this has been phased out. I have recently been working on a Square backed project, which uses this same iframe approach, but you cannot customize the fields or do any kind of validation: you just get the textboxes they give you with no way to add in things like specialized input types for numbers to help on mobile. To Stripe's credit, they at least go through the trouble of adding more intelligent validation & input handling. Will give this a closer look and may replace the Square version.