[Webkit-unassigned] [Bug 256814] New: Safari 16.4 changed parsing of style background-position with missing semicolon

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=256814

            Bug ID: 256814
           Summary: Safari 16.4 changed parsing of style
                    background-position with missing semicolon
           Product: WebKit
           Version: Safari 16
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: DOM
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkitbugzilla at intensity.org.uk

This behaviour changed with the introduction of Safari 16.4. It is still present in Safari technology Preview Release 169 (Safari 16.4, WebKit 18616.1.12.2)

Given the following HTML:

    <div id="outer" style="background-position: 10% 0%"></div>

Note the missing semicolon at the end of the style definition.

In Safari 16.4, this node's style.cssText becomes "background-position: 10%;"
In older Safari or any other browser, this node's style.cssText is "background-position: 10% 0%;"

Visible reproducer at https://jsfiddle.net/shadowphiar/skh5q6yz/


The reason this matters is that if any other style gets applied (such as a rotation transform) and background-position is recalculated, then suddenly the background-position-y is treated as 50% (because now only one argument is present in background-position). The writer expects background-position-y to remain 0%. I understand that the markup is incorrect but treating it so differently will be very unexpected.

This currently affects a production site boardgamearea.com and in particular their implementation of the game Carcassonne.

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