[css3-mediaqueries] serializing unknown media type

I noticed that IE9 is a bit different from other browsers in that it
serializes an arbitrary media type as "unknown" instead of the original
input.

This turns out, as far as I can tell, not to create a non-conforming
case as css3-mediaqueries doesn't say very clearly that a UA has to
store the unknown media types. Some options:

A. Don't change the spec and keep it as it is.

B. Explicitly ask UA to store an unknown media type. Concrete proposal:

In 3.1. Error Handling,

change

  # Unknown media types. Unknown media types evaluate to false.
  # Effectively, they are treated identically to known media types that
  # do not match the media type of the device.

to (be more clarified)

  | Unknown media types. Unknown media types evaluate to false.
  | Effectively, they are treated identically to known media types that
  | do not match the media type of the device, which means that a UA
  | must store an unknown media type so that it is accessible via
  | CSSOM.

C. Make it undefined.

(I think an explicit undefined is usually better than saying nothing at
all.)

Just in case we want a "mixed approach", these are all the media types
IE9 recognizes: ‘aural’, ‘braille’, ‘handheld’, ‘print’, ‘projection’,
‘screen’, ‘tty’, ‘tv’ and ‘embossed’. Or in other words, all the media
types listed in css3-mediaqueries besides 'speech'.


Cheers,
Kenny