[css3-writing-modes] available vs fill-available and multiple specs with definitions

The writing mode spec and box model spec differ on what this new keyword is
supposed to be called.

http://dev.w3.org/csswg/css3-writing-modes/ => fill-available
http://dev.w3.org/csswg/css3-box/ => available

Gecko currently implements -moz-available

Which is correct?

Also which spec should be considered as being more accurate for the
description of these new properties and how they interact?

- Elliott