files/en-us/web/http/reference/headers/observe-browsing-topics/index.md
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[!WARNING] This feature is currently opposed by two browser vendors. See the Standards positions section for details of opposition.
The HTTP Observe-Browsing-Topics {{Glossary("response header")}} is used to mark topics of interest inferred from a calling site's URL (i.e., the site where the ad tech {{HTMLElement("iframe")}} is embedded) as observed in the response to a request generated by a feature that enables the Topics API.
The browser will subsequently use those topics to calculate top topics for the current user for future epochs.
See Using the Topics API for more details.
<table class="properties"> <tbody> <tr> <th scope="row">Header type</th> <td> {{Glossary("Response header")}} </td> </tr> </tbody> </table>Observe-Browsing-Topics: ?1
?1
<iframe> is embedded) are marked as observed. The browser will subsequently use those topics to calculate topics of interest for a user for future epochs.This feature is not part of an official standard, although it is specified in the Topics API Unofficial Proposal Draft.
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