In addition to general purpose elements such as paragraphs and lists, HTML documents can express hyperlinks. An HTML user agent allows the user to navigate these hyperlinks.
A hyperlink is a relationship between two anchors, called the head and the tail of the hyperlink[DEXTER]. Anchors are identified by an anchor address: an absolute Uniform Resource Identifier (URI), optionally followed by a '#' and a sequence of characters called a fragment identifier. For example:
http://www.w3.org/hypertext/WWW/TheProject.html http://www.w3.org/hypertext/WWW/TheProject.html#z31
In an anchor address, the URI refers to a resource; it may be used in a variety of information retrieval protocols to obtain an entity that represents the resource, such as an HTML document. The fragment identifier, if present, refers to some view on, or portion of the resource.
Each of the following markup constructs indicates the tail anchor of a hyperlink or set of hyperlinks:
These markup constructs refer to head anchors by a URI, either absolute or relative, or a fragment identifier, or both.
In the case of a relative URI, the absolute URI in the address of the head anchor is the result of combining the relative URI with a base absolute URI as in [RELURL]. The base document is taken from the document's <BASE> element, if present; else, it is determined as in [RELURL].