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

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).

Start with the control-value() definition in Overview.html, then review the referenced progress and meter elements and their value, position, max, and min attributes. Resolve whether the function applies to these elements and specify which normalized or raw value it should return, including the edge cases described in the issue; the definition should state the resulting behavior.