Why don't Base64 Embedded fonts work in IE11 if "font download" property is disabled?

Question

So at face value, this makes sense -- if IE disables "font download," it shouldn't download, fine, I accept that.

HOWEVER -- what about using base64 fonts? These are embedded directly in CSS / do not reference a physical file, therefore no font should need to be downloaded, right?

At first I thought that maybe IE11 didn't like/support base64, but I can verify that it does work there when I use only a base64 font option.

I wasn't able to find any specs on this, or much info on the breadth of what "font download: disable" really means. I did see some similar posts but with no answers, and not asking the same question.

Anyone have a better explanation for this?

Answer 1

Per a memo on the base64 spec:

6. Security

   Interpretation of the data within a "data" URL has the same security considerations as any implementation of the given media type. An application should not interpret the contents of a data URL which is marked with a media type that has been disallowed for processing by the application's configuration.

Sources: http://www.ietf.org/rfc/rfc2397.txt http://sosweetcreative.com/2613/font-face-and-base64-data-uri