[css-forms-1] What does control-value() return for `<progress>` and `<meter>`?

[lukewarlow]

Currently, control-value() is defined to only return a value for a "form control" (which isn't defined). I'm assuming this should be more generic and work for at least the <progress> and presumably <meter> elements too?

If we assume that it does work, what does it return?

<progress value="25" max="50"> - given this element the value property in fact returns 25, but the position property returns 50 (which is the rendered progress of the control), Should control-value() match value proper, or position?

For <progress> doing that maths yourself is on the surface quite easy but there's various edge cases that the browsers IDL properties handle for you which it would be good to avoid needing to write JS or the logic in CSS.

For <meter> it's even more complicated by the addition of the min attribute into the mix (progress always has a minimum of 0).

[nt1m]

control-value() should return whatever .value returns. You can use attr() to reflect the attribute value.

[lukewarlow]

Thing is if the attribute value is invalid the browser has an algorithm to determine a fallback value. To implement that in CSS would be messy, especially for UA styles.

[nt1m]

I would have thought .value (not .getAttribute("value")) handled fallback and validation?

[lukewarlow]

Sorry to clarify I mean it doesn't handle the maths to get the progress value for you and if we don't have a way to access the internal min and max values too then you'd have to access the attrs.

[nt1m]

Oh, I see what you mean. I do think we should try to match the JS attribute for simplicity of understanding and let folks do the maths with the attr() function. Mainly because the main use case for control-value() at the moment is reflecting the value.

One thing that we could consider is adding an argument to control-value() that would get the normalized value?

[lukewarlow]

Is there maybe a usecase for exposing more than one internal value? Based on an argument?

Or perhaps if they ask for a percentage they can get the "position" value rather than raw value?

Just thinking how would we do a UA style to do the sizing for the progress element.