[Webkit-unassigned] [Bug 217900] New: CSS property "border-image" is not behaving correctly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=217900

            Bug ID: 217900
           Summary: CSS property "border-image" is not behaving correctly
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Macintosh
                OS: macOS 10.15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: Richard at Hallas.net

Created attachment 411733

  --> https://bugs.webkit.org/attachment.cgi?id=411733&action=review

Screenshot of Safari Technology Preview Release 114 (Safari 14.1, WebKit 15611.1.1.3) compared with Firefox 81.0.2; Firefox displays the border-image box correctly whereas Safari displays nothing.

Many pages on the website at www.careyblyton.com use border-image either to put a box around a block of fixed text at the top-right of the page, or to create a vertical divider between page areas. For example, on the page https://careyblyton.com/??=OpenLetter, the main area scrolls but there's a fixed block of text in the top-right corner, and this fixed text should be surrounded by a border.

The relevant CSS style definition includes the following code:
…
        -webkit-border-image: url(../img/border.png) 16 repeat;
        -moz-border-image: url(../img/border.png) 16 repeat;
        -o-border-image: url(../img/border.png) 16 repeat;
        border-image: url(../img/border.png) 16 repeat;
…

Safari, of course, correctly ignores the -moz- and -o- entries. However, the presence of border-image, which is now officially supported, also causes the -webkit-border-image line (included for compatibility with earlier versions of Safari) to be ignored. That is, Safari appears to obey the border-image line rather than the -webkit-border-image line… which in theory is indeed the correct behaviour.

Unfortunately, in reality, the -webkit-border-image line produces the correct effect, whereas the border-image line does not. If the border-image line is disabled, so that Safari falls back to observing the -webkit-border-image line, the results are correct. But if the border-image line is present and observed, Safari simply displays no border.

No other browser has this bug; Chrome, Brave, Vivaldi, Opera, Edge, Firefox etc. all display correctly.

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