Fix selection.modify() to use resolved text direction instead of inline base direction

[sambandaru]

Steps 7–8 of Selection.modify() use the inline base direction (paragraph-level CSS direction) to map "left"/"right" to forwards/backwards. This is wrong when the caret is inside a bidi run with a different direction.

<p dir="ltr">Hello שלום world</p>

When the caret is inside "שלום" (an RTL run) and the user presses the Right arrow, the current spec maps Right to forwards, and moves the caret visually to the left. This is incorrect.

The spec should instead use the resolved text direction at the caret (rtl), which maps Right to backwards and moves the caret visually to the right.

Fix: Replace "inline base direction" with "resolved text direction at the focus" (bidi embedding level per UAX#9: even = LTR, odd = RTL).

Browser behavior: Firefox and Safari already use resolved text direction. Chromium currently matches the spec text; a fix is in progress. This change aligns the spec with majority interoperable behavior.

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Preview | Diff

[sambandaru]

@rniwa Could you please review

[rniwa]

For normative changes, the following tasks have been completed:

• Editing WG resolution on the proposed changes, with at least two implementers participating and not objecting:

  • WebKit
  • Chromium
  • Gecko

• For browsers that are shipping the feature, implementation bugs are filed for the proposed changes (link to bug, or write "Not Implementing"):

  • WebKit (https://bugs.webkit.org/show_bug.cgi?id=)
  • Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
  • Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

[rniwa]

Please file bugs for each browser and have this discussed at an editing WG meeting.

[sambandaru]

For normative changes, the following tasks have been completed:

• Editing WG resolution on the proposed changes, with at least two implementers participating and not objecting:

  • WebKit
  • Chromium
  • Gecko

• For browsers that are shipping the feature, implementation bugs are filed for the proposed changes (link to bug, or write "Not Implementing"):

  • WebKit (https://bugs.webkit.org/show_bug.cgi?id=)
  • Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
  • Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

• WebKit (Already shipped)
• Chromium (https://issues.chromium.org/issues/499819853)
• Gecko (Already shipped)

[sambandaru]

Please file bugs for each browser and have this discussed at an editing WG meeting.

Ack

[smaug----]

Are there WPT tests for this?

[sambandaru]

Are there WPT tests for this?

I will add one.