Hypertext Links

The anchor <A> element is used to define the start and/or destination of a hypertext link. In previous versions of HTML it provided the only means for defining destination anchors within documents, but you can now use any ID attribute as a destination anchor so that links can now be made to divisions, paragraphs and most other elements.

Example:

The <A HREF="http://www.w3.org/">World Wide Web Organization</A>
provides information on Web related standards, mailing lists
and freeware tools.

The text between the start and end tag defines the label for the link. Selecting the link takes the reader to the document specified by the HREF attribute, in this case, the W3O home page. The label can include graphics defined with IMG elements.

For FIG elements, the anchor element serves a dual role. Non-graphical user agents interpret it as a conventional text-based hypertext link, while graphical user agents interpret the anchor's SHAPE attribute as a graphical hotzone on the figure.

Permitted Attributes

ID

An SGML identifier used as the target for hypertext links or for naming particular elements in associated style sheets. Identifiers are NAME tokens and must be unique within the scope of the current document. This attribute supercedes the "NAME" attribute, see below.

For example, the following paragraph is defined as an anchor named "potomac":

<P ID="potomac">The Potomac river flows into Boston harbour,
and played an important role in opening up the hinterland
to early settlers...

Elsewhere, you can define a link to this paragraph, as follows:

<A HREF="#potomac">Boston</A> is a historic city and
a thriving center of commerce and higher education.

The reader can select the link labelled "Boston" to see further information on the Boston area.

LANG

This is one of the ISO standard language abbreviations, e.g. "en.uk" for the variation of English spoken in the United Kingdom. It can be used by parsers to select language specific choices for quotation marks, ligatures and hypenation rules etc. The language attribute is composed from the two letter language code from ISO 639, optionally followed by a period and a two letter country code from ISO 3166.

CLASS

This a space separated list of SGML NAME tokens and is used to subclass tag names. By convention, the class names are interpreted hierarchically, with the most general class on the left and the most specific on the right, where classes are separated by a period. The CLASS attribute is most commonly used to attach a different style to some element, but it is recommended that where practical class names should be picked on the basis of the element's semantics, as this will permit other uses, such as restricting search through documents by matching on element class names. The conventions for choosing class names are outside the scope of this specification.

HREF

The HREF attribute implies that the anchor acts as the start of a hypertext link. The destination is designated by the value of the HREF attribute, which is expressed in the Universal Resource Identifier (URI) notation.

MD

Specifies a message digest or cryptographic checksum for the linked document designated by the HREF attribute. It is used when you want to be sure that a linked object is indeed the same one that the author intended, and hasn't been modified in any way. For instance, MD="md5:jV2OfH+nnXHU8bnkPAad/mSQlTDZ", which specifies an MD5 checksum encoded as a base64 character string. The MD attribute is generally allowed for all elements which support URI based links.

NAME

This attribute is used to define a named anchor for use as the destination of hypertext links. For example, the following defines an anchor than can be used as the destination of a jump into a description of the Boston area.

The <A NAME="potomac">Potomac river</A> flows into Boston
harbour.

Note: the NAME attribute has been superceded by the ID attribute. User agents should include support for NAME to ensure backwards compatibility with legacy documents produced using previous versions of HTML.

SHAPE

This attribute is used within figures to define shaped hotzones for graphical hypertext links. Full details of how to use this feature will be given with the description of the figure element. The attribute value is a string taking one of the following forms:

"default"

Used to define a default link for the figure background.

"circle x, y, r"

Where x and y define the center and r specifies the radius.

"rect x, y, w, h"

Where x, y define the upper left corner and w, h define the width and height respectively

"polygon x1, y1, x2, y2, ..."

Given n pairs of x, y coordinates, the polygon is closed by a line linking the n'th point to the first. Intersecting polygons use the non-zero winding number rule to determine if a point lies inside the polygon.

If a pointer event occurs in a region where two or more shapes overlap, the distance from the point to the center of gravity of each of the overlapping shapes is computed and the closest one chosen. This feature is useful when you want lots of closely spaced hotzones, for example over points on a map, as it allows you to use simple shapes without worrying about overlaps.

Note: The x coordinate increases to the right, and the y coordinate increases downwards in the same way as IMG and image maps. If both numbers are integers, the coordinates are interpreted as pixel offsets from the upper left corner of the figure. Otherwise, the coordinates are interpreted as scaled values in the range 0.0 to 1.0 across the figure. Note the syntax is tolerant of repeated white space characters between tokens.

TITLE

This is informational only and describes the object specified with the HREF attribute. It can be used for object types that don't possess titles, such as graphics, plain text and Gopher menus.

REL

Used to describe the relationship of the linked object specified with the HREF attribute. The set of relationship names is not part of this specification, although "Path" and "Node" are reserved for future use with hypertext paths or guided tours. The REL attribute can be used to support search for links serving particular relationships.

REV

This defines a reverse relationship. A link from document A to document B with REV=relation expresses the same relationship as a link from B to A with REL=relation. REV=made is sometimes used to identify the document author, either the author's email address with a mailto URI, or a link to the author's home page. Tables of contents can use anchors with REV="ToC" to allow software to insert page numbers when printing hypertext documents. The plain text version of this specification was generated in this way!