supported-color-schemes

The value defines the default supported color schemes for the document and allow the UA to know what backdrop color to draw early on to avoid white flash before rendering a dark themed document. The value must be a set of space-separated tokens, each matching a <color-scheme> production for the supported-color-schemes CSS property, or an ASCII case-insensitive match for only.

Issue: This is based on the current Safari behavior, but Safari also recognizes commas as separators. See WebKit issue.

The user agent is expected to treat these tokens as a presentational hint setting the root element's supported-color-schemes property to a space separated list as follows:

  1. Add all tokens which match the <color-scheme> production.
  2. If the list is still empty, add light.
  3. If the set of tokens contains an ASCII case-insensitive match for only, add only.

If a meta element is inserted into the document, or an existing meta element in a document tree have its content attribute changed, and the element has a name attribute whose value is an ASCII case-insensitive match for supported-color-schemes, user agents must set the default supported color schemes for that element's node document from the content attribute.

This document only supports dark theming:

<!DOCTYPE HTML>
               <meta name="supported-color-schemes" content="dark">
               ...

This document supports both light and dark theming:

<!DOCTYPE HTML>
               <meta name="supported-color-schemes" content="dark light">
               ...