Should serialization of @page selectors include "@page"?

[dbaron]

w3c/web-platform-tests#6183 points out that:

• there is currently lack of interop in how CSSPageRule.selectorText's getter serializes @page selectors
• the spec for this is currently just an issue saying the text needs to be written

Given that there is lack of interop today as to whether a rule

@page :left {
  margin: 0;
}

should serialize the selector text through CSSPageRule.selectorText as @page :left or :left, it seems like the WG should agree on which is the right behavior.

I tend to think that serializing to :left is the right thing to do, but given that implementations currently differ, I think it's worth bringing to the WG.

[dbaron]

I wrote a test to check browser behavior.

[dbaron]

• WebKit gives @page :left.
• Chromium gives :left.
• Gecko doesn't implement @page selectors, so the rule is dropped
• Edge gives an empty string for selectorText (but does parse the rule -- it doesn't parse the rule for @page foo, though)

(My preference is still the Chromium behavior.)

[dbaron]

@litherum @smfr do you think WebKit would be ok with changing behavior here?

[tabatkins]

Chrome's behavior seems like the obviously correct one.

[mstensho]

Gecko now supports (for some time already, for all I know) @page selectors and CSSPageRule, and serializes @page :left as :left (CSSPageRule.selectorText) - just like Chromium. WebKit still serializes as @page :left