Document Render Blocking #245
Labels
from: Google
Proposed, edited, or co-edited by Google.
topic: html
Spec relates to HTML (Hypertext Markup Language)
venue: WHATWG HTML Workstream
venue: WICG
Proposal is incubated in the Web Incubator Community Group
WebKittens
@smfr
Title of the spec
HTML
URL to the spec
whatwg/html#9332
URL to the spec's repository
No response
Issue Tracker URL
No response
Explainer URL
https://github.com/WICG/view-transitions/blob/main/document-render-blocking.md
TAG Design Review URL
w3ctag/design-reviews#886
Mozilla standards-positions issue URL
mozilla/standards-positions#875
WebKit Bugzilla URL
No response
Radar URL
No response
Description
The Web is designed with a model for incremental rendering. When a Document is loading, the browser can render its intermediate states before fetching all the requisite sub-resources, executing all script or fetching/parsing the complete Document. While this is great to reduce the time for first paint, there is a tradeoff between showing a jarring flash of intermediate Document state (which could be unstyled or have more CLS) vs blocking rendering on high priority sub-resources within a reasonable timeout.
The render-blocking concept helps browsers in making this tradeoff. It lets authors specify the set of stylesheets and script elements which should block rendering. For example, a stylesheet with the rules necessary to ensure a stable layout. But authors can’t specify which nodes should be added to the DOM before first render. This proposal aims to fill this gap.
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