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Hyperlink

Method of referencing visual computer data

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The document containing a hyperlink is known as its source document. For example, in content from Wikipedia or Google Search, many words and terms in the text are hyperlinked to definitions of those terms. Hyperlinks are often used to implement reference mechanisms such as tables of contents, footnotes, bibliographies, indexes, and glossaries.

In some hypertext, hyperlinks can be bidirectional: they can be followed in two directions, so both ends act as anchors and as targets. More complex arrangements exist, such as many-to-many links.

The effect of following a hyperlink may vary with the hypertext system and may sometimes depend on the link itself; for instance, on the World Wide Web most hyperlinks cause the target document to replace the document being displayed, but some are marked to cause the target document to open in a new window (or, perhaps, in a new tab). Another possibility is transclusion, for which the link target is a document fragment that replaces the link anchor within the source document. Not only persons browsing the document may follow hyperlinks. These hyperlinks may also be followed automatically by programs. A program that traverses the hypertext, following each hyperlink and gathering all the retrieved documents is known as a Web spider or crawler.

An inline link displays remote content without the need for embedding the content. The remote content may be accessed with or without the user following the link.

An inline link may display a modified version of the content; for instance, instead of an image, a thumbnail, low resolution preview, cropped section, or magnified section may be shown. The full content is then usually available on demand, as is the case with print publishing software – e.g., with an external link. This allows for smaller file sizes and quicker response to changes when the full linked content is not needed, as is the case when rearranging a page layout.

An anchor hyperlink (anchor link) is a link bound to a portion of a document, which is often called a fragment. The fragment is generally a portion of text or a heading, though not necessarily. For instance, it may also be a hot area in an image (image map in HTML), a designated, often irregular part of an image.

Fragments are marked with anchors (in any of various ways), which is why a link to a fragment is called an anchor link (that is, a link to an anchor). For example, in XML, the element <anchor id="name" />" provides anchoring capability (as long as the DTD or schema defines it), and in wiki markup, {{anchor|name}} is a typical example of implementing it. In word processor apps, anchors can be inserted where desired and may be called bookmarks. In URLs, the hash character (#) precedes the name of the anchor for the fragment.

One way to define a hot area in an image is by a list of coordinates that indicate its boundaries. For example, a political map of Africa may have each country hyperlinked to further information about that country. A separate invisible hot area interface allows for swapping skins or labels within the linked hot areas without repetitive embedding of links in the various skin elements.

Text hyperlink. Hyperlink is embedded into a word or a phrase and makes this text clickable.

Image hyperlink. Hyperlink is embedded into an image and makes this image clickable.

Bookmark hyperlink. Hyperlink is embedded into a text or an image and takes visitors to another part of a web page.

E-mail hyperlink. Hyperlink is embedded into e-mail address and allows visitors to send an e-mail message to this e-mail address.

A fat link (also known as a "one-to-many" link, an "extended link" or a "multi-tailed link") is a hyperlink which leads to multiple endpoints; the link is a set-valued function.

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