Sec-CH-Prefers-Reduced-Transparency user agent client hint request header indicates the user agent's preference for reduced transparency.
If a server signals to a client via the
Accept-CH header that it accepts
Sec-CH-Prefers-Reduced-Transparency, the client can then respond with this header to indicate the user's preference for reduced transparency. The server can send the client appropriately adapted content — for example, CSS or images — to reduce the transparency of the content.
This header is modeled on the
prefers-reduced-transparency media query.
The user agent's preference for reduced transparency. This is often taken from the underlying operating system's setting. The value of this directive can be either
The client makes an initial request to the server:
GET / HTTP/1.1 Host: example.com
The server responds, telling the client via
Accept-CH that it accepts
Sec-CH-Prefers-Reduced-Transparency. In this example
Critical-CH is also used, indicating that
Sec-CH-Prefers-Reduced-Transparency is considered a critical client hint.
HTTP/1.1 200 OK Content-Type: text/html Accept-CH: Sec-CH-Prefers-Reduced-Transparency Vary: Sec-CH-Prefers-Reduced-Transparency Critical-CH: Sec-CH-Prefers-Reduced-Transparency
Note: We've also specified
Sec-CH-Prefers-Reduced-Transparency in the
Vary header, to indicate to the browser that the served content will differ based on this header value — even if the URL stays the same — so the browser shouldn't just use an existing cached response and instead should cache this response separately. Each header listed in the
Critical-CH header should also be present in the
The client automatically retries the request (due to
Critical-CH being specified above), telling the server via
Sec-CH-Prefers-Reduced-Transparency that it has a user preference for reduced transparency:
GET / HTTP/1.1 Host: example.com Sec-CH-Prefers-Reduced-Transparency: "reduce"
The client will include the header in subsequent requests in the current session unless the
Accept-CH changes in responses to indicate that it is no longer supported by the server.
|User Preference Media Features Client Hints Headers |
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