Better define Print "formatting hints"

https://w3c.github.io/webdriver/#print-page has:

In addition, the following formatting hints should be applied by the UA:

If scale is not equal to 1:
Zoom the size of the content by a factor scale

If background is false:
Suppress output of background images

If shrinkToFit is true:
Resize the content to match the page width, overriding any page width specified in the content

These seem basically entirely undefined.

What does "zoom the size of the content" mean? Does this effectively just "set the zoom property on the root element"?

While "suppress output of the background images" is clear, I expect we should actually just define this by reference to https://drafts.csswg.org/css-color-adjust-1/#propdef-print-color-adjust (which is admittedly very open-ended!).

"Resize the content to match the page width" is also incredibly vague. Like, we're always setting a page width and height, thus aren't we setting the size of the page box, and thus the content won't be larger than the width?

Start with the WebDriver print-page section cited in the issue and compare its definitions of scale, background, and shrinkToFit with the CSS Color Adjustment print-color-adjust definition. Clarify the intended browser behavior and specify each hint precisely enough for interoperable implementations; the issue is done when the specification text no longer relies on the noted ambiguities.