Compression Dictionary Transport

The rel attribute defines the relationship between a linked resource and the current document. Valid on <link>, <a>, <area>, and <form>, the supported values depend on the element on which the attribute is found.

The type of relationships is given by the value of the rel attribute, which, if present, must have a value that is an unordered set of unique space-separated keywords. Differently from a class name, which does not express semantics, the rel attribute must express tokens that are semantically valid for both machines and humans. The current registries for the possible values of the rel attribute are the IANA link relation registry, the HTML Living Standard, and the freely-editable existing-rel-values page in the microformats wiki, as suggested by the Living Standard. If a rel attribute not present in one of the three sources above is used some HTML validators (such as the W3C Markup Validation Service) will generate a warning.

The following table lists some of the most important existing keywords. Every keyword within a space-separated value should be unique within that value.

rel value Description <link> <a> and <area> <form>

alternate Alternate representations of the current document. Link Link Not allowed

author Author of the current document or article. Link Link Not allowed

bookmark Permalink for the nearest ancestor section. Not allowed Link Not allowed

canonical Preferred URL for the current document. Link Not allowed Not allowed

compression-dictionary Link to a compression dictionary that can be used to compress future downloads for resources on this site. Link Not allowed Not allowed

dns-prefetch Tells the browser to preemptively perform DNS resolution for the target resource's origin. External Resource Not allowed Not allowed

external The referenced document is not part of the same site as the current document. Not allowed Annotation Annotation

expect When used with blocking="render", allows the page to be render-blocked until the essential parts of the document are parsed so it will render consistently. Link Not allowed Not allowed

help Link to context-sensitive help. Link Link Link

icon An icon representing the current document. External Resource Not allowed Not allowed

license Indicates that the main content of the current document is covered by the copyright license described by the referenced document. Link Link Link

manifest Web app manifest. Link Not allowed Not allowed

me Indicates that the current document represents the person who owns the linked content. Link Link Not allowed

modulepreload Tells to browser to preemptively fetch the script and store it in the document's module map for later evaluation. Optionally, the module's dependencies can be fetched as well. External Resource Not allowed Not allowed

next Indicates that the current document is a part of a series and that the next document in the series is the referenced document. Link Link Link

nofollow Indicates that the current document's original author or publisher does not endorse the referenced document. Not allowed Annotation Annotation

noopener Creates a top-level browsing context that is not an auxiliary browsing context if the hyperlink would create either of those, to begin with (i.e., has an appropriate target attribute value). Not allowed Annotation Annotation

noreferrer No Referer header will be included. Additionally, has the same effect as noopener. Not allowed Annotation Annotation

opener Creates an auxiliary browsing context if the hyperlink would otherwise create a top-level browsing context that is not an auxiliary browsing context (i.e., has "_blank" as target attribute value). Not allowed Annotation Annotation

pingback Gives the address of the pingback server that handles pingbacks to the current document. External Resource Not allowed Not allowed

preconnect Specifies that the user agent should preemptively connect to the target resource's origin. External Resource Not allowed Not allowed

prefetch Specifies that the user agent should preemptively fetch and cache the target resource as it is likely to be required for a followup navigation. External Resource Not allowed Not allowed

preload Specifies that the user agent must preemptively fetch and cache the target resource for current navigation according to the potential destination given by the as attribute (and the priority associated with the corresponding destination). External Resource Not allowed Not allowed

prerender Specifies that the user agent should preemptively fetch the target resource and process it in a way that helps deliver a faster response in the future. This feature is superseded by the Speculation Rules API. External Resource Not allowed Not allowed

prev Indicates that the current document is a part of a series and that the previous document in the series is the referenced document. Link Link Link

privacy-policy Gives a link to information about the data collection and usage practices that apply to the current document. Link Link Not allowed

search Gives a link to a resource that can be used to search through the current document and its related pages. Link Link Link

stylesheet Imports a style sheet. External Resource Not allowed Not allowed

tag Gives a tag (identified by the given address) that applies to the current document. Not allowed Link Not allowed

terms-of-service Link to the agreement, or terms of service, between the document's provider and users who wish to use the document. Link Link Not allowed

The rel attribute is relevant to the <link>, <a>, <area>, and <form> elements, but some values only relevant to a subset of those elements. Like all HTML keyword attribute values, these values are case-insensitive.

The rel attribute has no default value. If the attribute is omitted or if none of the values in the attribute are supported, then the document has no particular relationship with the destination resource other than there being a hyperlink between the two. In this case, on <link> and <form>, if the rel attribute is absent, has no keywords, or if not one or more of the space-separated keywords above, then the element does not create any links. <a> and <area> will still created links, but without a defined relationship.