[CSS Foldable Primitives] `spanning:none` behavior

[zouhir]

spanning:none can mean 2 things:

1. the browser window is not spanning, period.
   in that case we match: desktops, smartphones, tablets, as well as dual-screen & foldable devices when the browser is not spanned across the 2 display region.

2. the browser window is not spanning, but the device can span
   in this case we should only match a dual-screen or foldable-device where the browser can span, but it's not spanned at the moment.

today we it matches option 1, but I think it should match option 2.

use case
a web game with a specific layout that is optimized for dual-screen experience, where the controller needs to be visible at the bottom screen and game play on the top, might want to be able to ask the user to span or rotate their device.

[darktears]

I think I'm leaning towards option two as well. In the @media (spanning: none) you typically do two things:

• Reset the state to a single segment when you leave the spanning mode.
• Invite the user (banner or other mean) to span the window because you provide a better experience when spanning.

I think it's weird that the code in that block would get parsed and resolved in desktop/mobile/tablet etc where clearly, it's not applicable.