[Webkit-unassigned] [Bug 84543] New: unicode-bidi:plaintext treats embedded element with unicode-bidi:plaintext or isolate incorrectly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=84543

           Summary: unicode-bidi:plaintext treats embedded element with
                    unicode-bidi:plaintext or isolate incorrectly
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: aharon at google.com
                CC: playmobil at google.com, xji at chromium.org,
                    rniwa at webkit.org, leviw at chromium.org
            Blocks: 50910


The current definition of unicode-bidi:plaintext in CSS Writing Modes Level 3 states:

This value behaves as ‘isolate’ except that for the purposes of the Unicode bidirectional algorithm, the base directionality of each bidi paragraph immediately contained by the element is determined not by the element's computed ‘direction’ as usual, but by following the heuristic in rules P2 and P3 of the Unicode bidirectional algorithm. An element immediately contains a bidi paragraph if the element itself, but none of its descendants, both contains the entire bidi paragraph and is either a block container or a bidi-isolating inline.

Thus, if you have inline element A around inline element B, where A has unicode-bidi:plaintext and B has unicode-bidi:isolate, then:

1. The paragraphs in B must get their base direction from B's direction property as usual, not from their content as would be the case if B has unicode-bidi:plaintext - even though B is inside A and A does have unicode-bidi:plaintext. The "immediately contained" definition was recently added to clarify this very point.

2. B's content must not affect the direction of the paragraph in A inside which B occurs (because, according to the spec, "for the purpose of bidi resolution in its containing bidi paragraph (if any), [an element with unicode-bidi:isolate] is treated as if it were an Object Replacement Character (U+FFFC)"). The same is true if B also had unicode-bidi:plaintext (because unicode-bidi:plaintext "behaves as ‘isolate’").

Unfortunately, neither 1 nor 2 holds in WebKit. The first two attachments show this when A is a block element. (I used a <div> with unicode-bidi:-webkit-isolate style, but it could have been done with a <pre> out of the box.) The next two attachment show that things are even worse when A is an inline element: the content after B completely disappears. Very strange and worrisome.

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