Add image-related Client Hints headers removed from the IETF draft

source

@@ -4021,6 +4021,18 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
     </ul>
    </dd>
 
+   <dt>Structured Headers</dt>
+
+   <dd>
+    <p>The following terms are defined in <cite>Structured Headers</cite>: <ref spec="STRUCTUREDHEADERS"></p>
+
+    <ul class="brief">
+     <li><dfn data-x-href="https://httpwg.org/http-extensions/draft-ietf-httpbis-header-structure.html#float">sh-float</dfn></li>
+     <li><dfn data-x-href="https://httpwg.org/http-extensions/draft-ietf-httpbis-header-structure.html#integer">sh-integer</dfn></li>
+    </ul>
+   </dd>
+
+
    <dt>Feature Policy</dt>
 
    <dd>
@@ -28595,6 +28607,47 @@ was an English &lt;a href="/wiki/Music_hall">music hall&lt;/a> singer, ...</pre>
 
   </div>
 
+  <h5>Image-related Client Hints request headers</h5>
+  There are several image-related Client Hints which enable proactive content negotiation of the
+  most adapted image based on the user's device characteristics. If these headers appear in a
+  request more than once or have multiple values, the server SHOULD only take the last value of the
+  last request header into account.
+
+  <h6>DPR</h6>
+  The “DPR” request header field is a number that indicates the client’s current Device Pixel
+  Ratio (DPR). Its value SHOULD be identical to `window.devicePixelRatio`.
+  <!-- TODO(yoav): Switch to link to the specific algorithm once one is exposed -->
+  <!-- TODO(yoav): change from SHOULD to "determine the value of DPR" kind of processing model -->
+
+  The header's value is a <code>sh-float</code>.
+
+  <h6>Viewport-Width</h6>
+  The “Viewport-Width” request header field is a number that indicates the layout viewport width
+  in CSS pixels. Its value SHOULD be the <span>viewport</span> width excluding the size of a
+  rendered scroll bar (if any), rounded to the smallest following integer (i.e. ceiling value).
+
+  The header's value is a <code>sh-integer</code>.
+
+  <h6>Width</h6>
+  The “Width” request header field is a number that indicates the desired resource width in CSS
+  pixels. Its value should be the initiator element's source set's source size, if one exists,
+  rounded to the smallest following integer (i.e. ceiling value).
+  <!-- TODO(yoav): once we define a proper algorithm, we need to pass the source-size from the caller into Fetch -->
+
+  The header's value is a <code>sh-integer</code>.
+
+  <h5>Image-related response headers</h5>
+  <h6>Content-DPR</h6>
+  The “Content-DPR” response header field is a number that indicates the received image's
+  <span>current pixel density</span>.
+
+  The header's value is a <code>sh-float</code>.
+  <!-- TODO(yoav): add a processing model that overrides the current pixel density with that value -->
+
+  The <span>current pixel density</span> affects the calculation of density corrected intrinsic
+  size of image resources. As a result, the server MUST explicitly indicate the DPR of the
+  selected image response whenever the DPR client hint was used, or when the server otherwise
+  modified the image dimensions to compensate for the device's screen density.
 
   <h5 id="alt">Requirements for providing text to act as an alternative for images</h5>
 
@@ -120676,6 +120729,10 @@ INSERT INTERFACES HERE
    <dt id="refsSRI">[SRI]</dt>
    <dd><cite><a href="https://w3c.github.io/webappsec-subresource-integrity/">Subresource Integrity</a></cite>, D. Akhawe, F. Braun, F. Marier, J. Weinberger. W3C.</dd>
 
+   <dt id="refsSTRUCTUREDHEADERS">[STRUCTUREDHEADERS]</dt>
+   <dd><cite><a href="https://httpwg.org/http-extensions/draft-ietf-httpbis-header-structure.html">Structured Headers</a></cite>, M. Nottingham, P-H. Kamp.</dd>
+
+
    <dt id="refsSVG">[SVG]</dt>
    <dd><cite><a href="https://svgwg.org/svg2-draft/">Scalable Vector Graphics (SVG) 2</a></cite>, N Andronikos, R. Atanassov, T. Bah, B. Birtles, B. Brinza, C. Concolato, E. Dahlström, C. Lilley, C. McCormack, D. Schepers, R. Schwerdtfeger, D. Storey, S. Takagi, J. Watt. W3C.</dd>