Intent to Prototype: Container Timing API

[Jase Williams]

Summary:
The Container Timing API enables monitoring when annotated sections of the DOM are displayed on screen and have finished their initial paint. A developer will have the ability to mark subsections of the DOM with the containertiming attribute (similar to elementtiming for the Element Timing API) and receive performance entries when that section has been painted for the first time. This API will allow developers to measure the timing of various components in their pages.

Bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=1940240

Specification:
https://github.com/bloomberg/container-timing (Soon to move into WICG first, then W3C)

Because of the similarities to Element Timing, this can't go directly into W3C. The working group are happy for work to continue in WICG first whilst we come up with a solution to potentially merge the two specifications in future. (See responses here: https://github.com/WICG/proposals/issues/260)

Standards Body:
W3C (Web Perf WG)

Platform Coverage:
all.

DevTools Bug:
N/A

Link to standards-positions discussion:
https://github.com/mozilla/standards-positions/issues/1155

Other Browsers:
Blink: Positive https://chromestatus.com/feature/5110962817073152
WebKit: considering

Preference:
dom.enable_container_timing

web-platform-tests:
https://wpt.fyi/results/container-timing/tentative?label=master&label=experimental&aligned&q=container%20timing

Bas Schouten has already provided a patch in the bug, this will be iterated on, alongside the specification which myself, Bas and others will be looking at.

Thanks!