What exactly does the 'only' keyword do in CSS media queries?

Question

On Mozilla\'s page about media queries, it says:

The only keyword hides style sheets from older browsers that don\'t support media queries:<

Answer 1

My guess is that certain pre-CSS3 browsers, which understand only media types, interpret

media="screen and (color)"
media="screen" // `screen` is a known media type; ACCEPT for screen media

and

media="only screen and (color)"
media="only"    // `only` is an unknown media type
media="unknown" // REJECT for any media

Essentially they ignore everything after the first space but treat the remainder as valid.