This request header contains the target selector for a successful fragment update.
Server-side code is free to optimize its response by only rendering HTML that matches the selector. For example, you might prefer to not render an expensive sidebar if the sidebar is not targeted.
Unpoly will usually update a different selector in case the request fails.
This selector is sent as a second header,
The user updates a fragment
Unpoly automatically includes the following request header:
The server chooses to render only the HTML for the updating fragment. It responds with the following HTTP:
Vary: X-Up-Target <div class="menu">...</div>
Request headers that influenced a response should be listed in a
Varyresponse header. This tells Unpoly to partition its cache for that URL so that each request header value gets a separate cache entries.
The server may change the render target context by including a CSS selector as an
in its response.
Content-Type: text/html X-Up-Target: .selector-from-server <div class="selector-from-server"> ... </div>
The frontend will use the server-provided target for both successful (HTTP status
and failed (status
The server may send an
X-Up-Target: :none response header with an empty body to skip the current render pass.
Also see skipping unnecessary rendering.