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Alex Danilochaals
Alex Danilo
authored and
chaals
committed
Referrer policy (#954)
* Added note that removes the restriction of <style> in <head> but pointing out that use in the body can trigger unwanted side effects. See Issue #544. * Added style to the set of flow content elements. * Partial commit for adding referrerpolicy. * Hard set for non-binary on the .include files, fixes merge pain. * Added attribute to stop git treating text files as binary. * Added referrer policy attribute for link reference resource fetch * Ported the commits from issue #560. Next, find other commits that this needs for completeness (attribute defs, IDL, etc.) * Addded definition section for referrer policy * Added a few more referrerpolicy references. * Bulk of referrerpolicy changes, check in for backup in reality. * Fixed up a bunch of link errors. * Fixed a few more linking errors, fixed typo. * Changes as per review, plus some markup cleanup.
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‎.gitattributes

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# - Deny applying with `git apply --whitespace=error-all`.
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# - Fix automatically with `git apply --whitespace=fix`.
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###############################################################################
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[attr]cleantext text eol=crlf whitespace=blank-at-eol,-blank-at-eof,-space-before-tab,tab-in-indent,tabwidth=4
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[attr]cleantext text eol=crlf whitespace=blank-at-eol,-blank-at-eof,-space-before-tab,tab-in-indent,tabwidth=4 -binary
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###############################################################################
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# DEFAULT VALUE

‎sections/attributes.include

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<td>Whether to allow the value to be edited by the user</td>
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<td><a>Boolean attribute</a></td>
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</tr>
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<tr>
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<th><code>referrerpolicy</code></th>
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<td><{a}>; <{area}>; <{iframe}>; <{img}>; <{link}></td>
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<td><a>Referrer policy</a> for <a>fetches</a> initiated by the element</td>
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<td><a>Referrer policy</a></td>
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</tr>
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<tr>
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<th><{links/rel}></th>
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<td><{a}>; <{area}>; <{link}></td>

‎sections/browsers.include

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<var>window</var>.
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4. Set the {{Document}}'s <a for="document">HTTPS state</a> to the
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[=response/HTTPS state=] of the resource used to generate the document.
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5. Execute the <a>Initialize a <code>Document</code>'s CSP list</a> algorithm on the {{Document}}
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5. Set the {{Document}}'s <a>referrer policy</a> to the result of
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parsing the <a><code>Referrer-Policy</code></a> header</a> of the <a>response</a>
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used to generate the document. [[!REFERRERPOLICY]]
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6. Execute the <a>Initialize a <code>Document</code>'s CSP list</a> algorithm on the {{Document}}
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object and the resource used to generate the document. [[CSP3]]
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6. Set [=the document's referrer=] to the
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7. Set [=the document's referrer=] to the
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<em>address of the resource from which Request-URIs are obtained</em> as determined when the
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fetch algorithm obtained the resource, if that algorithm was used and determined such a value;
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otherwise, set it to the empty string.
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7. <a>Implement the sandboxing</a> for the {{Document}}.
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8. If the <a>active sandboxing flag set</a> of the {{Document}}'s <a>browsing context</a> or any
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8. <a>Implement the sandboxing</a> for the {{Document}}.
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9. If the <a>active sandboxing flag set</a> of the {{Document}}'s <a>browsing context</a> or any
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of its <a>ancestor browsing contexts</a> (if any) have the
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<a>sandboxed fullscreen browsing context flag</a> set, then skip this step.
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‎sections/elements.include

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<{links/download}>;
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<{links/rel}>;
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<{links/hreflang}>;
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<{links/type}></td>
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<{links/type}>;
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<{link/referrerpolicy}></td>
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<td>{{HTMLAnchorElement}}</td>
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</tr>
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<{links/download}>;
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<{links/rel}>;
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<{links/hreflang}>;
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<{links/type}></td>
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<{links/type}>;
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<{link/referrerpolicy}></td>
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<td>{{HTMLAreaElement}}</td>
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</tr>
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<{iframe/sandbox}>;
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<{iframe/allowfullscreen}>;
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<{media/width}>;
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<{media/height}></td>
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<{media/height}>;
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<{iframe/referrerpolicy}></td>
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<td>{{HTMLIFrameElement}}</td>
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</tr>
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<{img/ismap}>;
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<{img/longdesc}>;
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<{media/width}>;
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<{media/height}></td>
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<{media/height}>;
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<{img/referrerpolicy}></td>
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<td>{{HTMLImageElement}}</td>
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</tr>
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<{link/crossorigin}>;
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<{link/rel}>;
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<{link/media}>;
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<{link/referrerpolicy}>;
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<{link/nonce}>;
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<{link/hreflang}>;
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<{link/type}>;

‎sections/infrastructure.include

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A <dfn for="document" lt="inserted into|inserted into the document|inserted into a document">node
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is inserted into a document</dfn> when the <a>insertion steps</a> are invoked with it as the
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argument and it is now <a>in a document tree</a>. Analogously, a
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<dfn for="document" lt="remove an element from a document|removed from a document|removed from">node
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<dfn for="document" lt="remove an element from a document|removed from a document|removed from the document|removed from">node
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is removed from a document</dfn> when the <a>removing steps</a> are invoked with it as the argument
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and it is now no longer in a <a>document tree</a>.
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* <a for="request">cache mode</a>
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* <a for="request">redirect mode</a>
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* <a>cryptographic nonce metadata</a>
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* <a for="request">referrer policy</a>
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* <a>parser metadata</a>
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:: The following terms are defined in <cite>Referrer Policy</cite> [[!REFERRERPOLICY]]
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* <a for="request">referrer policy</a>
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* The <dfn>`Referrer-Policy`</dfn> HTTP header
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* The <dfn>parse a referrer policy from a <code>`Referrer-Policy`</code> header</dfn> algorithm
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* The "<dfn><code>no-referrer</code></dfn>",
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"<dfn><code>no-referrer-when-downgrade</code></dfn>", and
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"<dfn><code>unsafe-url</code></dfn>" referrer policies
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: Web IDL
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:: The IDL fragments in this specification must be interpreted as required for conforming IDL
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fragments, as described in the Web IDL specification. [[!WEBIDL]]
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<i>missing value default</i>, used when the attribute is omitted, is the
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<dfn state for="cors">No CORS</dfn> state.
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<h4 id="referrer-policy-attributes">Referrer policy attributes</h4>
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A <dfn export="">referrer policy attribute</dfn> is an <a>enumerated attribute</a>.
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Each <a>referrer policy</a>, including the empty string, is a keyword for this attribute,
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mapping to a state of the same name.
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The attribute's <a>invalid value default</a> and <a>missing value default</a>
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are both the empty string state.
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The impact of these states on the processing model of various <a>fetches</a> is defined
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in more detail throughout this specification, in the WHATWG Fetch standard, and in <cite>Referrer Policy</cite>.
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[[!FETCH]] [[!REFERRERPOLICY]]
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<div class="note">
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Several signals can contribute to which processing model is used for a given <a>fetch</a>;
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a <a>referrer policy attribute</a> is only one of them. In general, the order in which these signals are processed are:
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<ol>
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<li>First, the presence of a <{link/}noreferrer}> link
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type;</li>
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<li>Then, the value of a <a>referrer policy attribute</a>;</li>
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<li>Then, the presence of any <{meta}> element with <a><code
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for="attr-meta-name">name</code></a> attribute set to <a><code>referrer</code></a>.</li>
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<li>Finally, the <code>`Referrer-Policy`</code> HTTP
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header.</li>
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</ol>
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</div>
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<h3 id="common-dom-interfaces">Common DOM interfaces</h3>
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<h4 id="reflecting-content-attributes-in-idl-attributes">Reflecting content attributes in IDL attributes</h4>

‎sections/semantics-document-metadata.include

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<dd><code>nonce</code> — Cryptographic nonce used in Content Security Policy checks [[CSP3]]</dd>
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<dd><code>hreflang</code> — Language of the linked resource</dd>
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<dd><code>type</code> — Hint for the type of the referenced resource</dd>
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<dd><code>referrerpolicy</code> - <a>Referrer policy</a> for <a>fetches</a> initiated by the element</dd>
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<dd><code>sizes</code> — Sizes of the icons (for <{link/rel}>="<code>icon</code>")</dd>
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<dd>
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Also, the <{link/title}> attribute has special semantics on this element: Title of the
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[CEReactions] attribute DOMString hreflang;
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[CEReactions] attribute DOMString type;
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[CEReactions, SameObject, PutForwards=value] readonly attribute DOMTokenList sizes;
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};
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[CEReactions] attribute DOMString referrerPolicy;
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};
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HTMLLinkElement implements LinkStyle;
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</pre>
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</dd>
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For <a>external resource links</a>, the <{link/type}> attribute is used as a hint to user agents
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so that they can avoid fetching resources they do not support.
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<!-- def <{link/referrerpolicy}> -->
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The <dfn element-attr for="link"><code>referrerpolicy</code></dfn> attribute is a
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<a>referrer policy attribute</a>. It is intended for use with <a>external resource links</a>,
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where it helps set the <a>referrer policy</a> used when <a>obtaining</a> the external resource.
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[[!REFERRERPOLICY]].
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The <dfn element-attr for="link"><code>title</code></dfn> attribute gives the title of the link.
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With one exception, it is purely advisory. The value is text. The exception is for style sheet
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<!-- def {{HTMLLinkElement/referrerPolicy}} -->
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The <dfn attribute for="HTMLLinkElement"><code>referrerPolicy</code></dfn> IDL attribute must
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<a>reflect</a> the <code>referrerpolicy</code>
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content attribute, <a>limited to only known values</a>.
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The IDL attribute <dfn attribute for="HTMLLinkElement"><code>relList</code></dfn> must
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<a>reflect</a> the <{link/rel}> content attribute.
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{{Window}} object's <a>environment settings object</a>.
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6. Set <var>request</var>'s <a>cryptographic nonce metadata</a> to the current state of the
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<{link}> element's <{link/nonce}> content attribute.
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7. <a>Fetch</a> <var>request</var>.
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7. Set <var>request</var>'s <a>referrer policy</a> to the current state of the
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<{link}> element's <{link/referrerpolicy}> content attribute.
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8. <a>Fetch</a> <var>request</var>.
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User agents may opt to only try to obtain such resources when they are needed, instead of
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pro-actively fetching all the external resources that are not applied.
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inappropriate keywords.
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</p>
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: <dfn><code>referrer</code></dfn>
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:: The value must be a <a>referrer policy</a>, which defines the default
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<a>referrer policy</a> for the <code>Document</code>. [[!REFERRERPOLICY]]
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If any <code>meta</code> elements are <a>inserted into the document</a> or
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<a>removed from the document</a>, or existing <code>meta</code> elements have their <code>name</code>
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or <code>content</code> attributes changed, user agents must run the following algorithm:
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1. <p>Let <var>candidate elements</var> be the list of all <code>meta</code> elements that
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meet the following criteria, in <a>tree order</a>:</p>
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<ul class="brief">
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<li>The element is <a>in a document tree</a></li>
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<li>The element has a <code>name</code> attribute, whose value is <code>referrer</code></li>
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<li>The element has a <code>content</code> attribute, whose value is not the empty string</li>
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<li>The element is a child of the <{head}> element of the document</li>
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</ul>
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2. For each <var>element</var> in <var>candidate elements</var>:
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1. <p>Let <var>value</var> be the value of <var>element</var>'s <code>content</code> attribute,
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converted to [=ASCII lowercase=].</p></li>
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2. <p>If <var>value</var> is one of the values given in the first column of the following
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table, then set <var>value</var> to the value given in the second column:</p>
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<table>
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<thead>
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<tr>
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<th>Legacy value
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<th>Referrer policy
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<tbody>
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<tr>
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<td><code>never</code>
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<td><code>no-referrer</code>
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<tr>
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<td><code>default</code>
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<td><code>no-referrer-when-downgrade</code>
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<tr>
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<td><code>always</code>
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<td><code>unsafe-url</code>
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<tr>
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<td><code>origin-when-crossorigin</code>
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<td><code>origin-when-cross-origin</code>
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</table>
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3. <p>If <var>value</var> is a <a>referrer policy</a>, then set <var>element</var>'s
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<a>node document</a>'s <a>referrer policy</a> to <var>policy</var>.</p>
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<p class="note">The fact that these steps are applied for each element enables <a
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href="https://w3c.github.io/webappsec-referrer-policy/#unknown-policy-values">deployment of
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fallback values for older user agents</a>. [[!REFERRERPOLICY]]</p>
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</div>
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<h5 id="other-metadata-names">Other metadata names</h5>
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<dfn lt="register the names|register the name|metadata names">Extensions to the predefined set of metadata names</dfn> may be registered in the

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