css.properties.display.is_transitionable — Safari 27 disables display transitions for popovers and <dialog>

What type of issue is this?

Incorrect support data (example: BrowserX says "86" but support was added in "40")

What information was incorrect, unhelpful, or incomplete?

What information is incorrect, unhelpful, or incomplete?

BCD currently lists css.properties.display.is_transitionable as supported in Safari since Safari 18:

safari": { "version_added": "18" }

This is no longer unconditionally true in Safari 27 / recent WebKit.

WebKit intentionally disabled display property transitions for popovers and

elements. As a result, display cannot participate in a discrete transition for these top-layer elements even when using:

What browsers does this problem apply to, if applicable?

Safari

What did you expect to see?

The Safari support data for css.properties.display.is_transitionable should reflect that support became partial in Safari 27 because display transitions are disabled for popovers and

.

Did you test this? If so, how?

A minimal test case can use a popover with an opacity + display transition:

<button popovertarget="popover">Toggle</button>

<div id="popover" popover>
  Popover content
</div>

#popover {
  opacity: 0;

  transition:
    opacity 500ms,
    display 500ms allow-discrete;

  &:popover-open {
    opacity: 1;

    @starting-style {
      opacity: 0;
    }
  }
}

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

WebKit commit: “Disable display property transitions for popover ...

Do you have anything more you want to share?

Meow

MDN URL

https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/transition-behavior

MDN metadata

MDN page report details

• Query: css.properties.transition-behavior
• Report started: 2026-09-17T07:54:12.299Z

Locate css.properties.display.is_transitionable in the browser-compatibility data and inspect the existing Safari entry. Read the linked WebKit commit for the affected popover and

behavior, then update Safari support to reflect the partial behavior beginning in Safari 27 and verify the data remains valid.