Upcoming WHATNOT meeting on 2026-05-07

[jstenback]

Today we held our weekly triage call, see #12401, and the meeting notes have been posted there.

The next one is scheduled for May 7th, 2026, at 9AM PT. Note that this is 1 week later in the AMER-EMEA friendly time.

People interested in attending the next call who need the invite: Please respond here or reach out on Chat. Please tag issues and PRs for the next call using agenda+ in all WHATWG repositories across issues and pull requests. We invite anyone who can contribute to join us.

[KurtCattiSchmidt]

I'd like to discuss bringing #10673 to Stage 3. The PR's are up to date and the boxes (other than implementor support) are all checked:

#12339
#11687

[jstenback]

Minutes:

• Issue 12309: Upstream Document Picture-in-Picture: Simon Pieters, who added the label for this issue, discussed the status of the Document Picture-in-Picture API, noting that Firefox and Chrome have implemented it. Apple has previously objected due to cross-platform concerns, especially regarding mobile devices, which currently only support the API on desktop in Chrome and Firefox. Anne van Kesteren suggested that extending the Media Session API could address the main use cases, such as custom controls and video ads, which are currently driving the need for Document Picture-in-Picture.
• API Approach and Use Cases for Picture-in-Picture: Simon Pieters noted that Document Picture-in-Picture has non-video use cases, like Google Maps, and that Google Meet uses it for controls in addition to video. Olli Pettay argued that the document Picture-in-Picture API is very reasonable and simpler than the video Picture-in-Picture API. Given that Firefox and Chrome are shipping this feature, the group decided to clarify the use cases and revisit the conversation in a future meeting to determine if the specification should be in a standards track or remain in WICG.
• Issue 11542: Out of Order HTML Streaming Parsing: Noam Rosenthal reported that they have been waiting for a response from Henri Sivonen (Mozilla) for a couple of months regarding this issue, which has a PR and is seeking stage three approval. Noam Rosenthal requested that if there is no response by the following meeting, the dependency on Henri should be removed and the group can decide on moving the issue to phase three. Anne van Kesteren was asked to review the PR, which involves changes related to processing instructions and template streaming.
• Issue 11478: Opaque Range Interface: Ana Sollano Kim reported that Stephanie, who brought up the issue, was not present at the meeting and that the issue might be a leftover from a previous discussion. Olli Pettay noted that the CSS part of the API has not been reviewed at all. Mason Freed emphasized that the request was to move to stage three, and Anne van Kesteren offered to try to find time to review it the following week.
• Issue 10378: Responsive Images and Alt Text for Video Poster: Scott Jehl, representing Squarespace, brought up this issue, which aims to extend the video poster attribute to support responsive images and art direction using the same capabilities as the <img> element. They explained two potential markup approaches: one using a child <img> element and an optional <picture> wrapper, and another using new attributes on the video and child source elements. Simon Pieters noted the proposal's relation to solving lazy loading for poster images, which involved an idea of using a poster-from-img attribute.
• Advancing Responsive Images for Video Poster to Stage One: Scott Jehl highlighted that an important secondary feature of this proposal is bringing alt text support to the poster image, which is currently unavailable. Johnny Stenback suggested that since there were no objections to solving the problem, and the issue description was updated with pros and cons, the proposal should move to stage one. Simon Pieters agreed with advancing the proposal to stage one.
• Issue 1861: Convenient Method to Stream a Response as Text: Noam Rosenthal proposed adding a textStream() method to the Response interface in Fetch to simplify the process of mediating between a response stream and a text-accepting stream like the new streaming HTML method. Anne van Kesteren suggested that this method should also be added to the Blob API and confirmed that the change would not be needed for Push Message API. Noam Rosenthal accepted the feedback and confirmed they would implement the changes in tandem for both Fetch and the File API.
• PR 1249: Add Platform Provided Behaviors for Custom Elements: Ana Sollano Kim provided an update on the proposal to add platform-provided behaviors, such as submit behavior, for custom elements, noting that a spec PR was published and feedback was addressed. They requested Anne van Kesteren to review the PR and requested to move to stage two. Anne van Kesteren expressed confusion about the API shape, suggesting that prior feedback recommended a more granular approach, which this proposal does not seem to adhere to.
• Granularity of Custom Element Behaviors: Mason Freed argued that the current proposal is appropriately granular, acting as an opt-in/opt-out mechanism that prevents developers from making mistakes that would occur with overly granular building blocks. Anne van Kesteren expressed concern that the current design is a "radical departure" from the custom elements philosophy of providing granular building blocks and may prevent developers from accomplishing certain use cases. Noam Rosenthal suggested that the proposed behaviors could be viewed as "presets" that developers can configure individually, similar to sanitizer presets, and that such an approach is a natural next step for the platform.
• Path Forward for Custom Element Behaviors: Ana Sollano Kim clarified that they included previous feedback and updated the proposal to address issues like composing behaviors and getting rid of a string API. They indicated that breaking down the submit behavior further could compromise accessibility. Mason Freed suggested updating the explainer with a sketch of how the presets and the lower-level quirks (like focusability) would interact, even if they cannot be fully specified yet. Ana Sollano Kim agreed to update the explainer, and Anne van Kesteren agreed to look into previous discussions that might be relevant to the proposal.
• PR 12124: Pass Correct Iframe Fallback URL to Resource Timing: Noam Rosenthal added this to the agenda because they were having difficulty getting reviews for this technical bug fix. Noam Rosenthal noted that Simon Pieters was not present and would follow up on Matrix.
• PR 11687: Declarative CSS Modules: Kurt Catti-Schmidt updated the group that this feature was recently moved to stage two and that they have addressed feedback on the two spec PRs. Kurt Catti-Schmidt requested discussion about meeting the criteria for stage three, which requires two implementers. Olli Pettay stated they would discuss the feature internally.