[css-om][css-backgrounds] Serialization of `background: none`

[nt1m]

Should background: none serialize to background: transparent or background: none ?

Latest STP serializes as transparent, whereas FF serializes as none.

@emilio @Loirooriol Wdyt?

[Loirooriol]

I guess this fits into the umbrella of #8155.
STP serializes as transparent because in WebKit/WebKit#9849 @darinadler interpreted that <'background-color'> appears 1st in grammar order. It's not completely clear, but it seems to me that the 1st one is actually <bg-image>.

[darinadler]

The reason you and I came to different conclusions, I suppose, is that background-color is the first item in the final item in the comma separated list of values, and bg-image is the first item in the non-final items. If there is only a single value and no comma, how does the grammar work, and make it valid without a comma, but bg-image counts as first? That’s where we didn’t understand it the same way.

[Loirooriol]

Mm, looking at it again, I'm less sure about it :)
If none is expected I would change the grammar to

<bg-layer>       = <bg-image> || <bg-position> [ / <bg-size> ]? || <repeat-style> || <attachment> || <box> || <box>
<final-bg-layer> = <bg-image> || <bg-position> [ / <bg-size> ]? || <repeat-style> || <attachment> || <box> || <box> || <'background-color'>

If transparent is expected, I would add a note or something.

[gsnedders]

see also #418 more generally about background serialisation

[css-meeting-bot]

The CSS Working Group just discussed [css-om][css-backgrounds] Serialization of `background: none` , and agreed to the following:

• RESOLVED: Move color at the end of the final-bg-layer grammar, to make it serialize as `none`

The full IRC log of that discussion

<emilio> TabAtkins: question is how does `background: none` serialize. Using shortest serialization and grammar is unclear
<emilio> ... because if you only specify one layer it matches final-background-layer and image-layer
<emilio> ... and since color is the first in the final-background-layer safari they serialize transparent
<emilio> ... other browsers serialize none
<emilio> ... proposal is to move color to the end of final-bg-layer
<emilio> ... which makes it serialize as none
<emilio> fantasai: I think it's great because it moves color to the end
<emilio> ... which makes sense because it's at the bottom
<emilio> ... but that would be a change to how a color + image serializes, and I'm not sure that's Web-compatible <emilio> RESOLVED: Move color at the end of the final-bg-layer grammar, to make it serialize as `none`

[tabatkins]

Not captured in the minutes - we're hoping this is web-compatible, since currently if you specify a color and an image, the color will serialize first.

[darinadler]

Not captured in the minutes - we're hoping this is web-compatible, since currently if you specify a color and an image, the color will serialize first.

Not sure that’s quite right: The specification says that, but do any web browsers currently do that?