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Component Internals>Preload>Prerender Explainer https://github.com/WICG/nav-speculation/blob/main/ua-initiated-prerendering.md Spec https://wicg.github.io/nav-speculation/prerendering.html Discussion about upstreaming into HTML and elsewhere: whatwg/html#7533 <https://github.com/whatwg/html/issues/7533> The corresponding TAG review is w3ctag/design-reviews#667 <https://github.com/w3ctag/design-reviews/issues/667>. (That review was for speculation-rules triggered prerendering, which has a superset of the considerations for omnibox-triggered prerendering.) Summary We would like to ship omnibox (i.e., URL bar) prerendering. With this feature, Chrome will start prerendering the high-confidence omnibox autocomplete suggestions. Chrome is currently prefetching resources for high-confidence suggestions using No-state Prefetch <https://developers.google.com/web/updates/2018/07/nostate-prefetch>, but with this feature we will be further processing the webpage, including the DOM tree construction and script execution. While this is a user agent feature, this is an observable change to the prerendered websites. This prerendering affects how the prerendered pages are processed. The website gets loaded before the navigation is committed, and the side-effects are delayed until activation (the actual navigation to the website was committed). We also would like to add a simple APIs (document.prerendering) to directly let the website know that it is being prerendered and when it was activated (prerenderingchange event, performance.activationStart timing). Note that we are not shipping speculation rules triggered prerender2 (I2E extension <https://groups.google.com/a/chromium.org/g/blink-dev/c/tcbtZoQIlvI/m/K26gVfbUAQAJ>) with this I2S, which allows web pages to prerender other web pages. We will come back (hopefully soon) with a separate I2S. For details about our web exposed changes shipping plan, please consult this doc: Interoperability Roadmap for Shipping Prerender2 Incrementally <https://docs.google.com/document/d/1GenZDPbTzRyp038gh8A_ylIoVTfKt40MFyg7Ek_7L58/edit> . Link to “Intent to Prototype” blink-dev discussion We don’t have a corresponding “Intent to Prototype”. This was implemented as a variation of other prerender2 triggers (Speculation rules I2E <https://groups.google.com/a/chromium.org/g/blink-dev/c/tcbtZoQIlvI/m/K26gVfbUAQAJ> ). Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)? We plan to roll out omnibox-triggered prerendering from Android platforms, where we already have the MPArch coverage. Eventually, we will enable this on all platforms. Demo link For a demo of prerendering generally, and its effect on websites, https://prerender2-specrules.glitch.me/ shows it triggered by speculation rules (which are not part of this Intent). Instruction: Demonstration of URL-bar-triggered Omnibox prerendering <https://docs.google.com/document/d/1sUbxYSu1o5G76tA4UW_xxgcfcOn8j6NlJc_Go0Gwb_Q/edit?usp=sharing> Demo page: https://omnibox-prerender.glitch.me/ Debuggability We are actively talking to the devtools team about adding general Prerender support to it [metabug <https://bugs.chromium.org/p/chromium/issues/detail?id=1217029>]. The MVP is to expose the prerendered page status in the panel so web developers can know if they finished successfully, or they couldn’t proceed due to its feature restrictions. We currently don’t have a plan to add devtools support specifically for the omnibox prerender trigger (your thoughts are welcome!). Measurement We have implemented UseCounters [cs <https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/public/mojom/web_feature/web_feature.mojom;l=3482>] to monitor the usage of the properties added by this I2S. Risks Compatibility There is a non-zero chance that the behavior of the prerendered sites can be broken. The prerendered pages are loaded and rendered before user actually navigates to the websites, so there will be some number of prerenders that are false positives, which end up not being used. The websites will observe the requests, and can run some JavaScript, which can have side effects. That said, triggering a prerender from the address bar isn’t an entirely new behavior. Chrome used to have a prerendering feature a long while ago <https://blog.chromium.org/2011/06/prerendering-in-chrome.html>. A similar behavior is also present in other browsers (e.g. “Preload Top Hit” feature in Safari). For omnibox prerendering, we minimize this by having a high confidence threshold value: We only issue prerendering for omnibox input that we are confident that the user will navigate to the page. Interoperability Gecko: Some informal positive discussion with Gecko engineers on the HTML Standard issue tracker <https://github.com/whatwg/html/issues/7533#issuecomment-1022051187> and in the HTML triage call <https://github.com/whatwg/html/issues/7488#issuecomment-1029510684>; formal positions request here: https://github.com/mozilla/standards-positions/issues/613 WebKit: WebKit already ships URL-bar triggered prerendering, but not any APIs for letting pages know about it, and it's unclear what strategy they are using to prohibit disruptive behaviors for prerendered pages. We have reached out for a formal positions request here in the hopes of moving toward interoperability: https://lists.webkit.org/pipermail/webkit-dev/2022-February/032113.html Web / Framework developers: N/A - The omnibox prerendering (scope of this I2S) is triggered without web author opt-in. See https://github.com/WICG/proposals/issues/2 for positive sentiments on speculationrules triggered prerendering. Ergonomics These features will be used by speculation rules-triggered prerender as well. Activation Developer activation is not needed. Omnibox prerendering is triggered by Chrome. Is this feature fully tested by web-platform-tests <https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>? Link to test suite results from wpt.fyi. It is not currently possible to trigger the omnibox prerendering path specifically from web platform tests. We have filed web-platform-tests/wpt#32726 <https://github.com/web-platform-tests/wpt/issues/32726> to discuss making it possible and will be working on driving that forward in collaboration with other browsers. In the meantime, we have written a lot of web platform tests using speculation rules as the trigger. These exercise many of the same code paths and can be adapted once an appropriate API is available for testing URL-bar-triggered prerendering: https://wpt.fyi/results/speculation-rules/prerender?label=experimental&label=master&aligned (Currently Chromium tests this using VirtualTestSuites [cs <https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/virtual/prerender/README.md>] instead of EnableExperimentalWebPlatformFeatures, so the tests are not green on wpt.fyi.) Entry on the feature dashboard <http://www.chromestatus.com/> https://chromestatus.com/feature/5710069172797440 -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAPVAxLVDPme9kEnB6NdeDHO6krO77D-GN8MMKzYAv8oLCyAtwA%40mail.gmail.com.
