[mediaqueries-4] Confused about the Boolean value of media features

[simevidas]

Section 2.4.2. Evaluating Media Features in a Boolean Context:

If the feature would be true for any value other than the number 0, a <dimension> with the value 0, or the keyword none, the media feature evaluates to true. Otherwise, it evaluates to false.

If I understand correctly, this means that if I, for example, wanted to determine whether (orientation) evaluates to true, I would have to check if at least one of (orientation: portrait) and (orientation: landscape) evaluates to true. If it does, that would meet the “any value” requirement mentioned in he quote above.

However, I’m having trouble finding the spec section that states that any keyword value other than none evaluates to true, which I assume to be the case. Could you point me in the right direction?

[simevidas]

Ah, I think I’ve figured it out. All keyword values with the exception of none evaluate to true, because they represent something that can be true in certain conditions. It is logically impossible for a keyword value to never be true, unless it were explicitly defined to never be true, which wouldn’t make sense.

[simevidas]

Ok, I think I’ve figured it out now. It depends on the environment in which the CSS is evaluated. So, for example, the pointer media feature accepts three values: none, coarse, and fine. In environments without a pointing device, both non-none values evaluate to false, and hence, (pointer) itself evaluates to false. On the other hand, in environments with any kind of pointing device, at least one of the non-none keywords will evaluate to true, and so (pointer) will be true, because it meets the “any value” requirement from the original quote above.

It makes sense in hindsight. I guess, my mistake was thinking that it should behave like JavaScript where a specific value is either always truthy or always falsy, but that’s not true for media feature keyword values whose Boolean value depends on the environment.

[tabatkins]

Yeah, the MQ keywords aren't variables, they're, well, queries. (orientation: landscape) is a question asking "is the orientation currently landscape?", which is either true or false, not something fetching the fixed-per-UA value of a landscape variable.