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|
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INTERNET DRAFT |
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|
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Hypertext links in HTML |
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draft-ietf-html-relrev-00.txt |
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|
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today |
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|
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Murray Maloney Liam Quin |
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SoftQuad Inc. SoftQuad Inc. |
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murray@sq.com lee@sq.com |
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|
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Status of this Memo |
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This document is an Internet Draft. Internet Drafts are |
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working documents of the Internet Engineering Task Force |
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(IETF), its Areas, and its Working Groups. Note that other |
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groups may also distribute working documents as Internet |
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Drafts. |
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|
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Internet Drafts are draft documents valid for a maximum of six |
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months. Internet Drafts may be updated, replaced, or |
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obsoleted by other documents at any time. It is not |
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appropriate to use Internet Drafts as reference material or to |
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cite them other than as a ``working draft'' or ``work in |
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progress.'' Please check the 1id-abstracts.txt listing |
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contained in the internet-drafts Shadow Directories on |
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nic.ddn.mil, venera.isi.edu, nnsc.nsf.net, nic.nordu.net, |
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ftp.nisc.sri.com, or munnari.oz.au to learn the current status |
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of any Internet Draft. |
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|
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This is a working document only, it should neither be cited |
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nor quoted in any formal document. |
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|
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This document will expire before 7 June 1996. |
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|
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Distribution of this document is unlimited. |
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|
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Please send comments to the author(s). |
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|
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Table of Contents |
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 |
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2. Anchors and Targets . . . . . . . . . . . . . . . . . . . . . 3 |
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2a. Anchors . . . . . . . . . . . . . . . . . . . . . . . . . 3 |
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2b. Targets . . . . . . . . . . . . . . . . . . . . . . . . . 4 |
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3. The LINK and A Elements and Their Attributes . . . . . . . . 5 |
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3a. The LINK Element . . . . . . . . . . . . . . . . . . . . . 5 |
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3b. The A Element . . . . . . . . . . . . . . . . . . . . . . 6 |
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3c. Common Attributes . . . . . . . . . . . . . . . . . . . . 6 |
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4. The REL and REV Attribute Values . . . . . . . . . . . . . . . 8 |
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4a. Legacy . . . . . . . . . . . . . . . . . . . . . . . . . . 8 |
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4b. Browser-defined Links . . . . . . . . . . . . . . . . . . 9 |
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4c. Navigational Node Links . . . . . . . . . . . . . . . . . 9 |
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4d. Hierarchy Links . . . . . . . . . . . . . . . . . . . . . 10 |
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4e. Sequence Links . . . . . . . . . . . . . . . . . . . . . . 11 |
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4f. Related Documents . . . . . . . . . . . . . . . . . . . . 12 |
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4g. Meta Documents . . . . . . . . . . . . . . . . . . . . . . 14 |
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4f. Other REL and REV Values Under Discussion . . . . . . . . 16 |
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5. Hypertext Includes . . . . . . . . . . . . . . . . . . . . . 18 |
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Murray & Quin [Page 1] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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5a. INCLUDE as a REL or REV Value . . . . . . . . . . . . . . 18 |
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5b. INCLUDE as an Element . . . . . . . . . . . . . . . . . . 19 |
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5c. SGML external entitities . . . . . . . . . . . . . . . . . 19 |
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6. Hypertext Paths . . . . . . . . . . . . . . . . . . . . . . . 19 |
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7. Proposed New Attributes for A and LINK Elements . . . . . . . 20 |
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7a. ACTION or STYLE or PROCESS or PRESENT . . . . . . . . . . 20 |
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7b. TARGET . . . . . . . . . . . . . . . . . . . . . . . . . . 21 |
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7c. DINGBAT . . . . . . . . . . . . . . . . . . . . . . . . . 21 |
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7d. HILITE or HIGHLIGHT . . . . . . . . . . . . . . . . . . . 21 |
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7e. METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . 22 |
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7f. SRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 |
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7g. WHEN . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 |
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7h. OBSOLETES, UPDATES and DERIVED-FROM: . . . . . . . . . . . 23 |
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8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23 |
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|
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Hypertext links in HTML |
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|
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This is a discussion paper: It was initiated through discussion on the |
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HTML Working Group mailing list. |
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|
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Hypertext link relationships, specified by using the REL and REV |
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attributes of the LINK and A elements, were conceived of as an early |
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feature of the HTML language. Amidst all of the various and sundry |
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efforts that have been undertaken to advance HTML and the World Wide |
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Web, the definition of a small set of widely accepted hypertext |
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relationships has yet to be agreed upon and deployed in user agents. |
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|
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Hypertext link relationships, and the attendant REL and REV attributes |
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of the LINK and A elements, are discussed in Dave Raggett's Internet |
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Draft on HTML 3.0. In addition, The Santa Cruz Operation, Inc (SCO) has |
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developed an HTML user agent, based on Mosaic, which incorporates the |
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use of the REL attribute of the LINK element. |
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|
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The first draft of this paper was based on Dave Raggett's paper and on |
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the author's experience with a partial implementation at SCO. Others |
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have contributed to the development of this paper through discussions on |
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the html-wg mailing list and through private correspondence with the |
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author. (See the Acknowledgements section.) |
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|
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1. Introduction |
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The hypertext link mechanism is the connective tissue used to weave |
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the World Wide Web. A hypertext link is an object which specifies |
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a connection between any arbitrary addressable objects, locations, |
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or resources. |
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|
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A hypertext link typically consists of an anchor and a target, each |
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of which may be further classified and between which relationships |
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may be identified. In HTML, there are several language elements |
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which are used to identify anchors and targets and thus support the |
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hypertext link mechanism. |
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|
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The anchor of a hypertext link is typically presented to the user, |
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through an HTML user agent, as a highlighted object (a word, phrase, |
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graphic image, etc.). Not all anchors of hypertext links must be |
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represented as highlighted within the document or the application. |
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An HTML user agent may, as appropriate, act upon a hypertext link by |
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taking immediate action, such as presenting a concurrent window. A |
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user agent may, in some cases, simply ignore an anchor and its |
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Murray & Quin [Page 2] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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hypertext link. |
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|
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An HTML user agent is free to provide whatever mechanism it chooses |
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to allow the user to traverse from anchor to target. Typically, |
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graphical applications provide for user interaction via a pointing |
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device such as a mouse. Typically, non-graphical text-based |
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applications provide for user interaction via keyboard and arrow |
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selection. |
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|
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Different hypertext links may have different behavior associated |
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with them. For example, a link to a Table of Contents may be |
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presented as an icon, with an appropriate label, in a tool bar. |
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Another application may present the same link as a simultaneous view |
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of the document in an alternate window or a concurrent pane. A |
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hypertext link may also initiate a software program, or present |
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audio, graphics, video, print, speech synthesis or braille. |
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|
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HTML provides a mechanism for specifying the relationship between an |
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anchor and a target as seen from either end of the hypertext link. |
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The LINK and the A elements each provide a REL and a REV attribute |
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which may be set with values to identify these relationships. The |
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IMG element and the SRC attribute can also be used to form links. |
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|
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This purpose of this document is to discuss and formalize hypertext |
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anchors as currently implemented on the World Wide Web, and to |
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propose REL/REV relationships that are useful and consistent with |
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current usage. This paper is intended to describe hypertext links, |
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anchors and targets, classes and relationships. It is also intended |
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to provide suggestions or hints for authors and publishers, and for |
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developers of HTML user agents to guide them in using the hypertext |
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link mechanism effectively. |
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|
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NOTE: This document does not address issues associated with |
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non-practiced usages of hypertext anchors, in particular the |
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inclusion/embedding of program applications (e.g. Java applets), |
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within HTML documents. |
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|
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2. Anchors and Targets |
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2a. Anchors |
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An anchor is any object which acts as a hypertext link to a |
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target. An anchor may be a highlighted phrase within an HTML |
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document, an icon on an HTML user-agent tool-bar or menu item, an |
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active graphic, or an image map. An anchor may also be an object |
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which is included by reference, such a graphic image. |
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|
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There are four ways to specify an anchor in HTML: |
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* the A element |
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* the LINK element |
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* the SRC attribute as used on |
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* the IMG element |
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* the UL element (HTML 3.0 proposal) |
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* the LI element (HTML 3.0 proposal) |
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* the NOTE element (HTML 3.0 proposal) |
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* the ISMAP attribute as used on the IMG element |
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|
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An anchor is typically specified using the A element. This form |
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of anchor is used to highlight an object (word, phrase, graphic |
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image, etc.) which may be activated by a user to traverse the |
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Murray & Quin [Page 3] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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link by using the following form: |
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<A HREF="target">object to highlight</A> |
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|
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An anchor may also be specified using the LINK element. This form |
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of anchor is used to establish a hypertext link between an entire |
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HTML document and another addressable object or resource. A LINK |
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element is considered document meta-information (it does not mark |
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a link relationship specific to any part of the body), and is |
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therefore restricted to lie within the document HEAD. Because |
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the LINK element is only allowed within the HEAD of an HTML |
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document, and because it has no content, it is not usually |
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represented within the body of an HTML document as seen through a |
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user agent. Its purpose is solely to inform the user agent that a |
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link exists. The user agent may process or ignore these links as |
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it sees fit, but it may, for example, present an icon on a |
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toolbar for the user to traverse the link. An example of LINK |
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usage is: |
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<LINK HREF="chapter1.html" REL=PREVIOUS> |
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<LINK HREF="chapter3.html" REL=NEXT> |
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|
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An anchor may also be specified using the IMG element. This form |
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of anchor is used to establish a hypertext link to include a |
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graphic image. Its purpose it solely to inform the user agent |
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that a graphic image may be placed at the current location if the |
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user agent is capable of doing so, and if the user has enabled |
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viewing of graphic images. An example of this form of IMG usage |
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is: |
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<IMG SRC="image.gif"> |
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|
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An anchor may also be specified by providing a value to the SRC |
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attribute on any HTML element which supports that attribute. |
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For example: |
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<NOTE CLASS=WARNING SRC=WARNING.gif> ... </NOTE> |
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|
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A specialized active hypertext link anchor known as an image map |
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may be specified by using the IMG element in combination with the |
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SRC and ISMAP attributes. An example of this form of IMG usage |
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is: |
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<A HREF="..."><IMG SRC="image.gif" ISMAP></A> |
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|
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2b. Targets |
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A target is any addressable object or resource which typically |
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serves as the destination of a hypertext link. The destination |
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may be another HTML document, a fragment within the same or |
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another HTML document, or any other type of object or resource. |
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|
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A target may also be an aggregate link which can be presented as |
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a list of possible targets from which a user can select. A Table |
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of Contents may be an example of an aggregate link. The result of |
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a query is an other example. |
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|
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Any addressable object may serve as the target of a hypertext |
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link. Typically, a target is addressed by specifying a URL/URI as |
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the value of an HREF or SRC attribute on HTML elements which |
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support those attributes. |
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|
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HTML also provides a number of language elements which may be |
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used to identify a target within an HTML document and to specify |
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Murray & Quin [Page 4] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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the base location from which relative addresses should be |
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formed. |
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|
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There are four ways to specify a target within an HTML document: |
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* the BASE element |
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* the NAME attribute of the A element |
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* the ID attribute of various elements, including A and LINK |
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(HTML 3.0 proposal) |
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* the NAME attribute of the LINK element |
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|
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The base location of a document may be recorded in the BASE |
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element in the HEAD of the document. The base location is the |
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address from which all relative URL addresses are to be formed. |
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For example: |
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<BASE HREF="http://server.domain/whatever"> |
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|
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A target may be specified by surrounding any object (word, |
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phrase, graphic image, etc.) with an A element having a non-null |
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NAME attribute, and the target is considered to be the beginning |
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of the encapsulated object. For example: |
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<A NAME="nametoken">target object</A> |
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|
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A target may also be specified by providing a value for the ID |
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attribute on any HTML element which supports that attribute. |
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For example: |
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<P ID="PARA-1.1"> |
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|
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A target may also be specified as an attribute to a LINK element. |
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A LINK element may only be used within the head of an HTML |
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document, and it has no content. For example: |
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<HTML> |
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<HEAD> |
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<LINK NAME="THIS"> |
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<LINK NAME="THAT" HREF="THAT.html"> |
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</HEAD> |
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|
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3. The LINK and A Elements and Their Attributes |
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The LINK and A elements share a set of common attributes. Except |
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where noted, the semantics of those attributes is the same. |
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|
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3a. The LINK Element |
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The LINK element indicates a hypertext link relationship between |
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the document in which it is found and some other object. Any |
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number of LINK elements may be used within the head of an HTML |
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document. The LINK element is empty (does not have a closing |
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tag). The LINK element takes the same attributes as the A |
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(anchor) element. |
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|
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The hypertext link described by the LINK element is not typically |
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represented within the text area of an HTML user agent. Instead, |
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an HTML user agent is free to either ignore any LINK element and |
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the hypertext link associated with it, or to represent the |
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hypertext link in some other way. |
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|
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Presenting hypertext links as active icons in a toolbar is one |
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way to present them to the user. Another may be to present the |
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target document in a concurrent window, such as with a table of |
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contents. |
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Murray & Quin [Page 5] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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|
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3b. The A Element |
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The A element is used to indicate the start (anchor) or end |
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(target) of a hypertext link within the body of an HTML |
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document. |
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|
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The hypertext link described by the A element is typically |
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represented as a highlighted object (word, phrase, graphical |
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image, etc.) within the text area of an HTML user agent. |
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|
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3c. Common Attributes |
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For the purposes of this discussion, the following is a list with |
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descriptions of the most important common attributes. All of the |
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attributes listed here are part of HTML 2.0 except for CLASS, ID |
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and MD, which are discussed in Dave Raggett's Internet Draft on |
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HTML 3.0. |
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|
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CLASS |
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The CLASS attribute value is used to subclass the hypertext |
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link. The CLASS attribute is most often used as a generalized |
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identifier to which style information may be attached by a |
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stylesheet mechanism. |
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|
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The CLASS attribute may also be used to subclass LINK |
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elements, thereby differentiating hypertext links with common |
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REL or REV values. This may provide unambiguous syntax, for |
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example, for multiple LINK elements with REL=NEXT within a |
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document. Thus, alternate paths through a document can be |
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coded within the document. For example: |
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<LINK REL=NEXT CLASS=NOVICE HREF=... > |
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<LINK REL=NEXT CLASS=VETERAN HREF=... > |
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<LINK REL=NEXT CLASS=EXPERT HREF=... > |
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<LINK REL=NEXT CLASS=GURU HREF=... > |
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|
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Multiple CLASS values may be specified. The potential list of |
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CLASS attribute values is open-ended. However, practical |
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application will likely require definition and specification |
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of at least a small set of accepted keywords, and agreement |
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on processing expectations for arbitrary keywords. The |
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keywords used in the previous example are typical of the |
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type of keywords which may be specified, but are not |
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proposed. |
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|
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HREF |
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The HREF attribute value specifies the location of a |
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destination or resource, expressed in the Universal Resource |
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Identifier (URI) notation. Only one HREF value may be |
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specified. An HTML user agent may present the value of the |
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HREF attribute in an information area when the user positions |
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the mouse over the anchor or otherwise indicates interest in |
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the anchor. |
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|
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ID |
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The ID attribute specifies an SGML identifier used as the |
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target of hypertext links or for naming particular elements |
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in associated style sheets. Only one ID value may be |
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specified. The attribute value must be unique within the |
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document. |
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Murray & Quin [Page 6] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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|
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MD |
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The MD attribute specifies a message digest or cryptographic |
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checksum for the target of the hypertext link. This attribute |
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is used by a user agent to verify that the linked object is |
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the same one that the author intended. |
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|
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NAME |
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The NAME attribute specifies a named location within an HTML |
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document and is used in forming addresses to target specific |
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locations within an HTML document. Only one NAME value may be |
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specified. The attribute value must be unique within the |
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document. |
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|
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REL |
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The REL attribute specifies the relationship of the target to |
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the anchor. For example, REL=NEXT is used to indicate that |
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the target is the next logical document in an author- |
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specified sequence. The REL attribute can also be used to |
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support search for links serving particular relationships. |
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|
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Multiple REL values may be specified. Aggregate links can be |
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formed by including multiple LINK elements with equivalent |
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REL values. Activating the link, in that case, may lead to a |
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virtual menu from which the user can make a selection. |
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|
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The nature of a link relationship is not always obvious from |
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the attribute value. Section 4 (Meaning of REL and REV |
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Attribute Values) describes commonly accepted values. |
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Designers of HTML user agents can use these descriptions as a |
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guide to implementation of browser or agent behavior. |
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|
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REV |
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The REV attribute specifies the relationship of the anchor to |
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the target. For example, REV=TOP is used to indicate that the |
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anchor is the top of an author-specified hierarchical tree |
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of which the target is a branch or node. |
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|
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Multiple REV values may be specified. A Table of Contents may |
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contain a series of anchors which specify REV=TOC. |
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|
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The nature of a link relationship is not always obvious from |
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the attribute value. Section 4 (Meaning of REL and REV |
410 |
Attribute Values) describes commonly accepted values. |
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Designers of HTML user agents can use these descriptions as a |
412 |
guide to implementation of browser or agent behavior. |
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|
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TITLE |
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The TITLE attribute is typically used to describe the linked |
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object specified by the HREF attribute. The attribute value |
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is a character string which may include spaces and |
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punctuation. An HTML user agent may present the value of the |
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TITLE attribute in an information area when the user |
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positions the mouse over the anchor or otherwise indicates |
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interest in the anchor. Authors/publishers can thereby |
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provide greater context to the user to aid them in making |
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decisions about whether to traverse a hypertext link. |
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|
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Murray & Quin [Page 7] |
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|
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INTERNET DRAFT Hypertext Links in HTML December 1995 |
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An HTML user agent may also use the value of the TITLE |
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attribute to set the value of an email subject field when the |
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HREF value uses the `mailto:' scheme. In this way, the |
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subject field may be preset with value that the author's mail |
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agent can recognize and process. |
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|
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Although the HREF and TITLE attributes have been singled out in |
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the list above, any of these attribute values may be presented in |
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an information area when the user positions the mouse over the |
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anchor or otherwise indicates interest in the anchor. For |
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example, an HTML user agent which is also an HTML editor may |
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display the value of ID or NAME attributes. |
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|
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4. The REL and REV Attribute Values |
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|
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The potential list of valid values for REL and REV is open-ended, |
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and this document is not intended to preclude the use or adoption of |
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other or additional values. In fact, it is anticipated that |
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hypertext applications which support specific knowledge domains will |
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need to develop specialized sets of keywords. It is hoped that the |
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development of extensions will not occur in isolation, and that |
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coordination of extensions among various interested parties will |
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prevent namespace contention or collision. |
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|
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Further, HTML user agents should continue to be liberal in accepting |
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new or alternate values, inasmuch as any name token is a legal |
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value. The HTML specification declares that REL/REV values are SGML |
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name tokens. That is, within the previously described syntactical |
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constraints, a REL or REV relationship value may be any arbitrary, |
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author-defined value that the author or publisher considers |
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important. In some cases, the HTML user agent may choose to present |
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relationships that it recognizes in a richer style, while |
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continuing to present unfamiliar ones in the default style. |
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|
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The REL and REV attributes are defined as NAMES in the SGML DTD for |
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the HyperText Markup Language (HTML). As such, the legal values |
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which may be assigned to the REL or REV attribute are zero or more |
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name tokens. Name tokens are case-insensitive, must begin with an |
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alpha character, may include digits (0-9), period or hyphen, and may |
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be separated by spaces. The name tokens listed and described in this |
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section are being recommended as commonly accepted relationships |
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between and among objects in a hypertext collection. |
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|
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When a single name token is specified as a REL or REV attribute, |
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double quotes surrounding the attribute value are optional. When |
473 |
multiple name tokens are specified, double quotes are mandatory. |
474 |
<A REL="PARENT" HREF="..." > previous </A> |
475 |
<A REL="PARENT PREVIOUS" HREF="..." > previous </A> |
476 |
<A REL="SIBLING NEXT" HREF="..." > next </A> |
477 |
|
478 |
4a. Legacy |
479 |
The following are REL values which were known to be used as |
480 |
values of the REL and REV attributes on the World Wide Web in |
481 |
December 1995. |
482 |
|
483 |
MADE |
484 |
The REV=MADE relationship has been used to identify the author |
485 |
or "maker" of an HTML document. Typical HREF values include a |
486 |
Murray & Quin [Page 8] |
487 |
|
488 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
489 |
`mailto:' URI or the URL of the author's home page. Example: |
490 |
<A REV=MADE HREF="mailto:murray@sq.com">Author</A> |
491 |
|
492 |
NEXT/PREVIOUS/TOC/INDEX/NAVIGATOR |
493 |
These values are described below, are used by SCO in its online |
494 |
documentation and context- sensitive help system. |
495 |
|
496 |
4b. Browser-defined Links |
497 |
|
498 |
Some keywords are reserved and should not be used as REL/REV |
499 |
values. |
500 |
|
501 |
HTML user agents typically provide a mechanism for navigating |
502 |
through the recent history of a user's access to documents; |
503 |
traditionally these operations are referred to as "back" and |
504 |
"forward". These mechanisms allow a user to step back through the |
505 |
documents which led to the current location and then forward |
506 |
again to retrace the path. Additionally, most user agents provide |
507 |
a mechanism to immediately return to a user-defined location, |
508 |
traditionally referred to as the home page, or "home". Since |
509 |
these browser actions are internally implemented by the browser, |
510 |
REL/REV keywords associated with these relationships are |
511 |
disallowed. |
512 |
|
513 |
HOME |
514 |
RESERVED. Defined by the user (for example, using an |
515 |
environment variable or preference, e.g. WWW_HOME). |
516 |
This relationship may not be overridden; HTML user agents |
517 |
should ignore any author-supplied REL=HOME setting. |
518 |
|
519 |
BACK |
520 |
RESERVED. Defined by the browser. This relationship may not |
521 |
be overridden; HTML user agents should ignore any |
522 |
author-supplied REL=BACK setting. |
523 |
|
524 |
FORWARD |
525 |
RESERVED. Defined by the browser. This relationship may not |
526 |
be overridden; HTML user agents should ignore any |
527 |
author-supplied REL=FORWARD setting. |
528 |
|
529 |
4c. Navigational Node Links |
530 |
Navigational nodes are commonly used document objects which are |
531 |
designed by authors to assist the user in navigating through a |
532 |
closed or extended document set. The most familiar and common |
533 |
form of navigational node is a table of contents, which is a well |
534 |
known publishing device used for enumerating and ordering the |
535 |
contents of a closed document set. |
536 |
|
537 |
CONTENTS or TOC |
538 |
The TOC relationship identifies a Table of Contents. |
539 |
|
540 |
When REL=TOC, the target document is the Table of Contents for |
541 |
the current document, or for the collection of documents of |
542 |
which the current document is a member. |
543 |
|
544 |
When REV=TOC, the current document is a Table of Contents and |
545 |
the target document is a related document. |
546 |
|
547 |
Murray & Quin [Page 9] |
548 |
|
549 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
550 |
When REL=TOC and REV=TOC it indicates that the current |
551 |
document is a Table of Contents and the target document is |
552 |
also a Table of Contents. Additional REL/REV values may be |
553 |
used to specify the relationship between the two, such as |
554 |
PARENT/CHILD. |
555 |
|
556 |
If the hypertext link is specified with REL in a LINK element, |
557 |
an HTML user agent may present an icon in a tool bar. Or, if |
558 |
capable, an HTML user agent may present the Table of Contents |
559 |
in a concurrent window or pane, highlighting the current |
560 |
document. |
561 |
|
562 |
INDEX |
563 |
The INDEX relationship identifies an index. |
564 |
|
565 |
When REL=INDEX, the target document is an index for the |
566 |
current document, or for the collection of documents of which |
567 |
the current document is a member. |
568 |
|
569 |
When REV=INDEX, the current document is an index. Additional |
570 |
REL/REV values may be used to further specify the relationship |
571 |
between the two ends of the link. |
572 |
|
573 |
If the hypertext link is specified with REL in a LINK element, |
574 |
an HTML user agent may present an icon in a tool bar. An index |
575 |
may be presented as an HTML document which is organized and |
576 |
presented in a style reminiscent of a paper-based index. An |
577 |
index may also be presented as a form-based query into a full- |
578 |
text search database. |
579 |
|
580 |
NAVIGATOR |
581 |
The NAVIGATOR relationship identifies a navigational aid. |
582 |
|
583 |
When REL=NAVIGATOR, the target document is a navigational aid. |
584 |
A navigational aid may consist of a whole or partial Table of |
585 |
Contents, a list of related documents, an indication of the |
586 |
current document's location within a document hierarchy, or |
587 |
any other information which may be useful to the user. |
588 |
|
589 |
When REV=NAVIGATOR, the current document is a navigational aid. |
590 |
|
591 |
If the hypertext link is specified with REL in a LINK element, |
592 |
an HTML user agent may present an icon in a tool bar. |
593 |
|
594 |
4d. Hierarchy Links |
595 |
It is quite common for documents to be developed or defined |
596 |
using a hierarchical model, or tree-like structure. The keywords |
597 |
listed below may be used within HTML documents to identify the |
598 |
hierarchical relationship of closely related nodes, such as the |
599 |
immediate parent, siblings and children. In addition, the TOP |
600 |
keyword may be used to identify the logical top (or root, |
601 |
depending on your perspective) of a hierarchical or tree-like |
602 |
structure. |
603 |
|
604 |
The entire set of relationships may be used by a user agent to |
605 |
build a map of the hierarchical structure(s) of which the |
606 |
current document is a node. Hypertext links to documents |
607 |
identified with PARENT and TOP values are more likely to be |
608 |
Murray & Quin [Page 10] |
609 |
|
610 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
611 |
accessible through an icon or other mechanism than documents |
612 |
identified with CHILD or SIBLING. |
613 |
|
614 |
CHILD |
615 |
The CHILD relationship identifies a subordinate or |
616 |
subdocument. Any document may have multiple CHILD documents |
617 |
within the same hierarchy. |
618 |
|
619 |
When REL=CHILD, the target document is a hierarchical child, |
620 |
or subdocument, of the current document. |
621 |
|
622 |
When REV=CHILD, the current document is the hierarchical |
623 |
child, or subdocument, of the target. |
624 |
|
625 |
PARENT |
626 |
The PARENT relationship identifies the superior or container |
627 |
node. |
628 |
|
629 |
When REL=PARENT, the target document is the hierarchical |
630 |
parent, or container, of the current document. |
631 |
|
632 |
When REV=PARENT, the current document is the hierarchical |
633 |
parent, or container, of the target. |
634 |
|
635 |
If the hypertext link is specified with REL in a LINK element, |
636 |
an HTML user agent may present an icon in a tool bar. |
637 |
|
638 |
SIBLING |
639 |
The SIBLING relationship identifies a sibling in the current |
640 |
hierarchy. Any document may have multiple SIBLING documents |
641 |
within the same hierarchy. |
642 |
|
643 |
When REL=SIBLING, the target document is a child of a common |
644 |
parent, or a hierarchical peer of the current document. REL |
645 |
and REV have equivalent meanings for the SIBLING |
646 |
relationship. |
647 |
|
648 |
TOP or ORIGIN |
649 |
The TOP relationship identifies the logical top of a |
650 |
hierarchical tree of which the current document is a branch. |
651 |
BEGIN is a functional equivalent to TOP, if only one of these |
652 |
values is specified. |
653 |
|
654 |
When REL=TOP, the target document is the logical top node of |
655 |
the tree. When REV=TOP, the current document is the logical |
656 |
top of the tree. |
657 |
|
658 |
If the hypertext link is specified with REL in a LINK element, |
659 |
an HTML user agent may present an icon in a tool bar. |
660 |
|
661 |
NOTE: ORIGIN has been suggested as an alternative to TOP to |
662 |
provide metaphorical consistency with PARENT/CHILD/SIBLING. |
663 |
Comments are encouraged. |
664 |
|
665 |
4e. Sequence Links |
666 |
Given a set of documents, it is possible and often desirable to |
667 |
specify linear sequences to navigate through the set. A book, for |
668 |
example, is often organized as a linear sequence. With sequence |
669 |
Murray & Quin [Page 11] |
670 |
|
671 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
672 |
links in each document, a user agent can step through or gather |
673 |
an entire book programmatically. |
674 |
|
675 |
BEGIN or FIRST |
676 |
The BEGIN relationship identifies the author- defined start of |
677 |
a sequence of documents of which the current document is a |
678 |
node. TOP is a functional equivalent to BEGIN when only one of |
679 |
these values is specified. |
680 |
|
681 |
When REL=BEGIN, the target document is the beginning of the |
682 |
sequence. When REV=BEGIN, the current document is the |
683 |
beginning of the sequence. |
684 |
|
685 |
If the hypertext link is specified with REL in a LINK element, |
686 |
an HTML user agent may present an icon in a tool bar. |
687 |
END or LAST |
688 |
The END relationship identifies the author defined end of a |
689 |
sequence of documents of which the current document is a node. |
690 |
TOP is a functional equivalent to END when only one is |
691 |
specified. |
692 |
|
693 |
When REL=END, the target document is the end of the sequence. |
694 |
When REV=END, the current document is the end of the sequence. |
695 |
|
696 |
If the hypertext link is specified with REL in a LINK element, |
697 |
an HTML user agent may present an icon in a tool bar. |
698 |
|
699 |
NEXT |
700 |
The NEXT relationship identifies the next document in an |
701 |
author-defined sequence of documents, such as a linear book. |
702 |
|
703 |
When REL=NEXT, the target document is next after the current |
704 |
document. When REV=NEXT, the current document is next after |
705 |
the target. |
706 |
|
707 |
If the hypertext link is specified with REL in a LINK element, |
708 |
an HTML user agent may present an icon in a tool bar. |
709 |
|
710 |
PREVIOUS or PREV |
711 |
The PREVIOUS relationship identifies the previous document in |
712 |
an author-defined sequence of documents, such as a linear |
713 |
book. |
714 |
|
715 |
When REL=PREVIOUS, the target document is previous to the |
716 |
current document. |
717 |
|
718 |
When REV=PREVIOUS, the current document is previous to the |
719 |
target. |
720 |
|
721 |
If the hypertext link is specified with REL in a LINK element, |
722 |
an HTML user agent may present an icon in a tool bar. |
723 |
|
724 |
4f. Related Documents |
725 |
BIBLIOENTRY |
726 |
The BIBLIOENTRY relationship identifies a bibliographic entry. |
727 |
|
728 |
BIBLIOENTRY would most typically be specified on an A element, |
729 |
as it would specify a hypertext link between a citation and a |
730 |
Murray & Quin [Page 12] |
731 |
|
732 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
733 |
bibliographic entry describing the citation. Example: |
734 |
<A REL=BIBLIOENTRY HREF="biblio.html#V.Bush"><CITE>As We |
735 |
May Think</CITE></A> |
736 |
|
737 |
The resource identified by this link may take any form desired |
738 |
by the author/publisher. A bibliographic entry may be presented |
739 |
in the style of a paper-based bibliographic entry, or it may be |
740 |
presented as the result of a database query. |
741 |
|
742 |
BIBLIOGRAPHY |
743 |
The BIBLIOGRAPHY relationship identifies a bibliography. |
744 |
|
745 |
The resource identified by this link may take any form desired |
746 |
by the author/publisher. A bibliography may be presented as an |
747 |
HTML document which is organized and presented in a style |
748 |
reminiscent of a paper-based bibliography. A bibliography may |
749 |
also be presented as a form-based query into a bibliographic |
750 |
database. |
751 |
|
752 |
If the hypertext link is specified with REL in a LINK element, |
753 |
an HTML user agent may present a labeled icon in a tool bar. |
754 |
|
755 |
CITATION |
756 |
The CITATION relationship identifies a bibliographic citation. |
757 |
|
758 |
When REL=CITATION, the target is a bibliographic citation. The |
759 |
anchor, in this case, may be a bibliographic entry. The anchor |
760 |
may also be a reference, thus allowing the reader a way to |
761 |
locate the citation: |
762 |
... as described by Tim Berners-Lee |
763 |
<A REL=CITATION HREF=#TBL>[1]</A> |
764 |
... |
765 |
|
766 |
When REV=CITATION, the anchor is a citation. Typically, the |
767 |
anchor would also be enclosed within a CITE element as shown in |
768 |
the example below. The example shown here also corresponds to |
769 |
the previous example, serving as its target by use of the NAME |
770 |
attribute. |
771 |
... is described in Tim Berners-Lee's |
772 |
<CITE><A NAME=TBL REV=CITATION HREF=./biblio/TBL > The |
773 |
HyperText Markup Language </A> </CITE> |
774 |
... |
775 |
|
776 |
NOTE: an alternative (and preferred) approach would be to add a |
777 |
URI-valued attribute (HREF?) to the HTML CITE element. |
778 |
|
779 |
DEFINITION |
780 |
The DEFINITION relationship identifies a definition of a term. |
781 |
|
782 |
Definitions may be, but are not necessarily, contained within a |
783 |
glossary. DEFINITION would most typically be specified on an A |
784 |
element, as it would specify a hypertext link from a term to |
785 |
its definition. |
786 |
<A REL=DEFINITION HREF="glossary.html#HTTP">HTTP</A> |
787 |
|
788 |
FOOTNOTE |
789 |
The FOOTNOTE relationship identifies a footnote. |
790 |
|
791 |
Murray & Quin [Page 13] |
792 |
|
793 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
794 |
When REL=FOOTNOTE is specified on an A element, the anchor is a |
795 |
footnote marker and the target is a footnote. This can be used |
796 |
to link from the footnote marker (or a highlighted word, |
797 |
phrase, etc.) to an HTML document which contains the footnote |
798 |
text, or to a portion of the same document (see REV=FOOTNOTE). |
799 |
|
800 |
When REL=FOOTNOTE is specified on a LINK element, it can |
801 |
specify a hypertext link to a set of footnotes which are |
802 |
related to the current document, or to a set of end-notes. |
803 |
|
804 |
When REV=FOOTNOTE is specified on an A element, the anchor is a |
805 |
footnote; that is, the actual content of the footnote, as |
806 |
opposed to a footnote marker. In this case, the target |
807 |
specified by the HREF value, if any, is the footnote marker. |
808 |
|
809 |
It has been suggested that the combination of REV=FOOTNOTE and |
810 |
NAME=... on an A element may be used to imply that the |
811 |
enclosed content not be rendered until a link to it is |
812 |
explicitly traversed, at which time it can be presented in a |
813 |
popup window. This would allow for the inclusion of footnote |
814 |
text within a document that would not be visible until the |
815 |
reader wanted it to be presented. Developers of user agents are |
816 |
free to experiment with this proposed feature, but there is no |
817 |
requirement that it be implemented. |
818 |
|
819 |
GLOSSARY |
820 |
The GLOSSARY relationship identifies a glossary. |
821 |
|
822 |
When REL=GLOSSARY, the target document is a glossary. When |
823 |
REV=GLOSSARY, the current document is a glossary. |
824 |
|
825 |
If the hypertext link is specified with REL in a LINK element, |
826 |
an HTML user agent may present an icon in a tool bar. |
827 |
|
828 |
A glossary may be directly presented as an HTML document which |
829 |
is organized and presented in a style reminiscent of a |
830 |
paper-based glossary. |
831 |
|
832 |
A glossary may also be accessed through an intermediary query |
833 |
mechanism. For example, the user highlights a word or phrase |
834 |
and presses the glossary button, thereby accessing the linked |
835 |
object and passing the highlighted text as an argument. The |
836 |
server returns the glossary entry relevant to the highlighted |
837 |
word. |
838 |
|
839 |
4g. Meta Documents |
840 |
There are classes of information which are not intrinsic to a |
841 |
document, but for which a clear and unambiguous association is |
842 |
often useful or even necessary. This section defines a small set |
843 |
of keywords which are related to ownership and legal notices. |
844 |
|
845 |
Any attempt to rigorously define a closed set of meta- data |
846 |
classes, types, and formats is doomed to failure, partly due to |
847 |
the need for ongoing experimentation. Hence, the META keyword |
848 |
may be used to identify meta documents which do not necesarily |
849 |
have a clear or unambiguous definition. The content of the target |
850 |
node may be as specific format as a MARC record or an FGDC |
851 |
record, or it may be an author-defined format. |
852 |
Murray & Quin [Page 14] |
853 |
|
854 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
855 |
|
856 |
For each of the relationship keywords listed in this section, if |
857 |
the relationship is specified with REL in a LINK element, an HTML |
858 |
user agent may present a labeled icon in a tool bar. |
859 |
|
860 |
AUTHOR |
861 |
The AUTHOR relationship identifies a hypertext link to |
862 |
an author. |
863 |
|
864 |
The hypertext link may be to the author's home page, a |
865 |
biography, an audio or video clip, or an agent which sends mail |
866 |
to the author (e.g., using the `mailto:' scheme). |
867 |
|
868 |
COPYRIGHT |
869 |
The COPYRIGHT relationship identifies a hypertext link to a |
870 |
copyright notice. |
871 |
|
872 |
While it is arguable whether a copyright notice is required in |
873 |
every HTML file to assert copyright protection on it, there is |
874 |
clearly a desire to express copyright notice among a sufficient |
875 |
portion of the user community to justify support. |
876 |
|
877 |
A basic copyright notice for this document may simply state: |
878 |
"Copyright 1995 by Murray C. Maloney". It may be desirable, |
879 |
in place of or in addition to such a notice, to have a |
880 |
hypertext link between each HTML document in a set and a single |
881 |
copyright notice, as in the following examples: |
882 |
<LINK REL=COPYRIGHT HREF="copyright.html"> |
883 |
<A REL=COPYRIGHT HREF="copyright.html"> |
884 |
Copyright 1995 by Murray C. Maloney</A> |
885 |
|
886 |
DISCLAIMER |
887 |
The DISCLAIMER relationship identifies a hypertext link to a |
888 |
legal disclaimer. Usage is expected to be similar to that of |
889 |
the COPYRIGHT hypertext link. As with the copyright notice, |
890 |
there is no intention or expectation that such a link would be |
891 |
the only way to express a disclaimer. |
892 |
|
893 |
EDITOR |
894 |
The EDITOR relationship identifies a hypertext link to an |
895 |
editor. Usage is expected to be similar to that of the AUTHOR |
896 |
hypertext link. |
897 |
|
898 |
META |
899 |
The META relationship identifies a hypertext link to a node |
900 |
which contains meta-information related to the current |
901 |
document. This is intended to be a generalized meta-data |
902 |
relationship descriptor. |
903 |
|
904 |
PUBLISHER |
905 |
The PUBLISHER relationship identifies a hypertext link to a |
906 |
publisher. Usage is expected to be similar to that of the |
907 |
AUTHOR hypertext link. |
908 |
|
909 |
TRADEMARK |
910 |
The TRADEMARK relationship identifies a hypertext link to a |
911 |
trademark notice. Usage is expected to be similar to that of |
912 |
the COPYRIGHT hypertext link. |
913 |
Murray & Quin [Page 15] |
914 |
|
915 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
916 |
|
917 |
4f. Other REL and REV Values Under Discussion |
918 |
The POINTER keyword is an invention of the author. |
919 |
|
920 |
The BANNER, BOOKMARK, HOTLIST and STYLESHEET keywords are |
921 |
described in Dave Raggett's Internet Draft on HTML 3.0. Recent |
922 |
discussions tend to indicate that these keywords may not be |
923 |
appropriate for use as REL/REV values. Dave Raggett's further |
924 |
explanation and justification is needed before any further |
925 |
discussion or decision can be made as to the future status of |
926 |
these keywords. |
927 |
|
928 |
The LANG attribute is described in Dave Raggett's Internet Draft |
929 |
on HTML 3.0. It has been applied to various HTML elements, not |
930 |
including the LINK and A elements. The author suggests that LANG |
931 |
is a useful attribute to apply to the LINK and A elements. See |
932 |
also the discussion of REL=TRANSLATION. |
933 |
|
934 |
BANNER |
935 |
The BANNER relationship identifies a document banner. |
936 |
|
937 |
When REL=BANNER, the target document is to be included within |
938 |
the current document as a banner. A banner is typically used |
939 |
for corporate logos, custom toolbars, and other information |
940 |
which would not typically be scrolled with the body of a |
941 |
document. |
942 |
|
943 |
When REV=BANNER, the current document is a banner. This may be |
944 |
used, in future, to provide error-checking or to prevent the |
945 |
use of a document as a banner unless it has been explicitly |
946 |
identified as a valid source. (Or not! Sorry, I was reaching |
947 |
for a useful meaning.) |
948 |
|
949 |
Compelling arguments have been made against the need for a |
950 |
REL=BANNER value, which is simply a special case of the INCLUDE |
951 |
mechanism. |
952 |
BOOKMARK |
953 |
The BOOKMARK relationship identifies a bookmark. |
954 |
|
955 |
Bookmarks are used to provide direct links to key entry points |
956 |
into an extended document. The TITLE attribute may be used to |
957 |
label the bookmark. Several bookmarks may be defined in each |
958 |
document, and provide a means for orienting users in extended |
959 |
documents. |
960 |
|
961 |
HOTLIST |
962 |
RESERVED: This keyword has been proposed by Dave Raggett. Its |
963 |
meaning and purpose require further explanation. A placeholder |
964 |
is being maintained until such time as Dave has had an |
965 |
opportunity to provide further explanation, examples, |
966 |
discussion and justification. |
967 |
|
968 |
If the hypertext link is specified with REL in a LINK element, |
969 |
an HTML user agent may present an icon in a tool bar. |
970 |
|
971 |
LANG |
972 |
The LANG attribute indicates the language of the target |
973 |
document. |
974 |
Murray & Quin [Page 16] |
975 |
|
976 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
977 |
|
978 |
The LANG attribute is optional and has no default value. It may |
979 |
be used for purely informational purposes by an HTML user |
980 |
agent, or by a robot for language classification. |
981 |
|
982 |
Used in combinatiuon with a proposed REL=TRANSLATION and a |
983 |
user's language preference setting, an HTML user agent may |
984 |
intelligently select from a collection of otherwise equivalent |
985 |
hypertext links expressed with the LINK element. If the user's |
986 |
language preference is not available, the user agent may |
987 |
present a virtual menu of language options. |
988 |
|
989 |
See the Internet Draft on the Internatiolisation of HTML for |
990 |
a definition of the values of this attribute. |
991 |
|
992 |
POINTER |
993 |
The pointer relationship identifies a hypertext pointer. That |
994 |
is, this is a way to do indirection in HTML. |
995 |
|
996 |
When REV=POINTER, the anchor is a pointer to the target |
997 |
document. When a hypertext link is traversed to a LINK or A |
998 |
element with REV=POINTER, the target specified by the HREF |
999 |
value should be traversed, and so on, until a target without |
1000 |
REV=POINTER is retrieved. |
1001 |
<LINK NAME=PSEUDO REV=POINTER HREF="real.html"> |
1002 |
|
1003 |
When REL=POINTER, the target is a pointer to the real target. |
1004 |
This value can be used by a user agent to perform a pre-fetch |
1005 |
of the specified target for evaluation until the real target is |
1006 |
reached. |
1007 |
|
1008 |
NOTE: The authors propose that the NAME attribute be removed |
1009 |
from the LINK element, or that a practical use for it should be |
1010 |
defined. For example, hypertext indirection can be specified by |
1011 |
providing both a NAME and an HREF value on the LINK element, in |
1012 |
combination with a specific REL or REV value, such as POINTER. |
1013 |
Some support exists among members of the HTML Working Group to |
1014 |
provide for hypertext indirection with the LINK element. There |
1015 |
is no other reason for an author to define a target by using |
1016 |
the NAME attribute on a LINK element, since the resulting |
1017 |
target address is functionally equivalent to the address of the |
1018 |
document in which such a target is defined. |
1019 |
|
1020 |
STYLESHEET |
1021 |
The STYLESHEET relationship identifies a stylesheet. |
1022 |
|
1023 |
When REL=STYLESHEET, the target document is a stylesheet. When |
1024 |
associated with a LINK element, the author/publisher is |
1025 |
expressing an expectation that the target stylesheet will be |
1026 |
applied by the HTML user agent. When associated with an A |
1027 |
element, an HTML user agent may simply retrieve the target |
1028 |
stylesheet for display, or it may launch a stylesheet editor |
1029 |
with the target stylesheet. |
1030 |
|
1031 |
When REV=STYLESHEET, the current document is a stylesheet and |
1032 |
the target document may be a demonstration of its use. In |
1033 |
general, it is not anticipated that stylesheets will contain |
1034 |
LINK or A elements, as they are not projected to be HTML |
1035 |
Murray & Quin [Page 17] |
1036 |
|
1037 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1038 |
documents. |
1039 |
|
1040 |
TRANSLATION |
1041 |
The TRANSLATION relationship specifies a translation to |
1042 |
another language. |
1043 |
|
1044 |
When REL=TRANSLATION, the target is a translation to another |
1045 |
language. This value will most typically be used with the LINK |
1046 |
element, in combination with specification of the target |
1047 |
document's language as a LANG attribute value. Presumably, |
1048 |
REL=TRANSLATION can be used with the A element to specify a |
1049 |
translation of a document fragment, such as a phrase in a |
1050 |
foreign language. |
1051 |
|
1052 |
When REV=TRANSLATION, the current document, or document |
1053 |
fragment, is a translation of the target. |
1054 |
|
1055 |
URC |
1056 |
The URC relationship identifies a Uniform Resource Catalogue |
1057 |
for the current document. |
1058 |
|
1059 |
This keyword has been proposed by Dave Raggett. Its meaning |
1060 |
and purpose have not been explained to the author, but a |
1061 |
placeholder is being maintained until such time as Dave has had |
1062 |
an opportunity provide explanation, examples, |
1063 |
discussion and justification. |
1064 |
|
1065 |
5. Hypertext Includes |
1066 |
There have been many discussions in various forums which clearly |
1067 |
indicate that hypertext includes are a desired feature of the HTML |
1068 |
language, and for which widespread user agent support is needed. |
1069 |
|
1070 |
There are, apparently, three popular syntactic approaches to |
1071 |
inclusion: specifying INCLUDE as REL value on the A and LINK |
1072 |
elements, specifying a newly-defined and specially- purposed INCLUDE |
1073 |
element (which would presumably also have REL and REV attributes), |
1074 |
and using SGML entities. Each is described and discussed below, but |
1075 |
no arguments are presented. |
1076 |
|
1077 |
In either case, there is an expectation that processing of an |
1078 |
INCLUDE link would result in the INCLUDE value being deleted from the |
1079 |
REL list and inserted into the REV list. In other words, a |
1080 |
REL=INCLUDE indicates that the inclusion has yet to happen, while a |
1081 |
REV=INCLUDE indicates that the inclusion has already happened. It is |
1082 |
helpful, for legal and copyright purposes, that included material be |
1083 |
identifiable at all times. |
1084 |
|
1085 |
Note that the form of inclusion referred to here is also known as |
1086 |
Transclusion, or as client side inclusion. It may happen either |
1087 |
automatically, when a document is loaded into an HTML client, |
1088 |
or explicitly: for example when the user selects an icon, included |
1089 |
text may appear at that point in the current document. |
1090 |
|
1091 |
5a. INCLUDE as a REL or REV Value |
1092 |
INCLUDE relationship identifies a document for inclusion. |
1093 |
|
1094 |
When REL=INCLUDE, the target document should be included at the |
1095 |
anchor location. This value is typically, though not always, used |
1096 |
Murray & Quin [Page 18] |
1097 |
|
1098 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1099 |
with the A element. Using this value on a LINK element implies |
1100 |
that the included document only contains information which is |
1101 |
valid within the HEAD of an HTML document. |
1102 |
|
1103 |
When REV=INCLUDE, the current document is identifying itself as an |
1104 |
included document in the target document. |
1105 |
|
1106 |
5b. INCLUDE as an Element |
1107 |
An anchor may also be specified using a newly-defined INCLUDE |
1108 |
element: |
1109 |
<INCLUDE REL=INCLUDE HREF="boilerplate.html"></INCLUDE> |
1110 |
|
1111 |
In this scheme, when the hypertext link is traversed, and the |
1112 |
content of the target document is included, the INCLUDE element |
1113 |
would surround the included text. As a function of traversing the |
1114 |
link, the REL attribute value would be transformed to a REV value, |
1115 |
thus maintaining information about the link. |
1116 |
<INCLUDE REV=INCLUDE HREF="boilerplate.html"> |
1117 |
This is the boilerplate text |
1118 |
</INCLUDE> |
1119 |
|
1120 |
5c. SGML external entitities |
1121 |
SGML provides a mechanism for specifying external entities and |
1122 |
including them, by reference, in an SGML document. |
1123 |
|
1124 |
Unfortunately, the current HTML browser technology cannot easily |
1125 |
support the use of SGML entities, and they cannot be used in |
1126 |
a way that is completely backwards-compatible with existing |
1127 |
software. |
1128 |
|
1129 |
6. Hypertext Paths |
1130 |
NOTE: Recent discussions tend to indicate that the mechanisms and |
1131 |
language uses needed to support paths have not been adequately |
1132 |
articulated or specified. This section appears here for historical |
1133 |
completeness. Dave Raggett's further explanation and justification is |
1134 |
needed before any further discussion or decision can be made as to |
1135 |
the future status of these keywords. |
1136 |
|
1137 |
Paths are described briefly in Dave Raggett's Internet Draft on HTML |
1138 |
3.0, and reproduced below without further explanation. Further |
1139 |
discussion, explanation and justification from Dave are clearly |
1140 |
required before any further public discussion or decision can be |
1141 |
made as to the future status of these keywords. The material below |
1142 |
is reproduced for historic purposes and may be subject to future |
1143 |
revision. |
1144 |
|
1145 |
Values for use in defining Guided Tours with <A> element. These |
1146 |
allow Guided Tours to be defined using HTML, for instance as part of |
1147 |
tables of contents, for example: |
1148 |
<A REL=NODE REV=TOC HREF="Chap1.html"> |
1149 |
|
1150 |
NODE |
1151 |
The NODE relationship implies PREVIOUS/NEXT LINKs for given URI. |
1152 |
|
1153 |
PATH |
1154 |
The PATH relationship specifies that the given URI contains <A |
1155 |
REL=NODE> links that should be inserted into the guided tour. |
1156 |
|
1157 |
Murray & Quin [Page 19] |
1158 |
|
1159 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1160 |
The browser treats the REL=NODE URIs as forming a sequence of |
1161 |
nodes to follow and sets the <LINK REL=PREVIOUS>, NEXT as |
1162 |
appropriate for each node as it is visited. |
1163 |
|
1164 |
7. Proposed New Attributes for A and LINK Elements |
1165 |
|
1166 |
Through the course of discussions, suggestions have been made to |
1167 |
create new attributes for the LINK and/or A elements. These are |
1168 |
preliminary discussions, with no sample implementations to |
1169 |
demonstrate support. |
1170 |
|
1171 |
7a. ACTION or STYLE or PROCESS or PRESENT |
1172 |
Activating a link in the HTML user agents of mid-1995 typically |
1173 |
results in the linked object replacing the current object in the |
1174 |
presentation window of the user agent. By convention, HTML user |
1175 |
agents typically provide an alternate method which spawns another |
1176 |
window and presents the linked object in it. |
1177 |
|
1178 |
It has been suggested by Ian Graham and Roy Fielding, and agreed |
1179 |
upon by many others, that the author should have some means to |
1180 |
indicate a preference for the manner in which the user agent |
1181 |
should present the linked object to the user. As you can see, the |
1182 |
name of the attribute still needs to be settled. |
1183 |
|
1184 |
From Ian Graham: It seems reasonable to allow the |
1185 |
author to suggest browser behavior when links are activated. |
1186 |
For example, when I click on a LINK button, should I clone a |
1187 |
window for the link, or pop up a subwindow for a glossary |
1188 |
entry? Perhaps this should be part of a CLASS attribute, but |
1189 |
to my mind CLASS should be used to define the |
1190 |
presentation/meaning of a document element in the document BODY |
1191 |
as opposed to browser behavior. |
1192 |
|
1193 |
And from Roy Fielding: Presentation semantics -- where should |
1194 |
the results be "placed". A `STYLE=""' attribute (defined as |
1195 |
SGML NAMES) would do nicely here. |
1196 |
|
1197 |
Possible values and their meanings are: |
1198 |
CLONE |
1199 |
Present the linked object in a presentation window which is a |
1200 |
clone of the current presentation window. That is popup another |
1201 |
persistent window. |
1202 |
|
1203 |
See the Netscape Frames proposal for one way to do this, using |
1204 |
named windows and the TARGET attribute described below. |
1205 |
|
1206 |
EMBED |
1207 |
Present the linked object at the current location. This |
1208 |
provides a syntax for expressing "stretch text", but it also |
1209 |
presents numerous problems. This will be subject to much |
1210 |
debate. See the section on Include, above. |
1211 |
|
1212 |
REPLACE |
1213 |
The default behavior. Present the linked object in the current |
1214 |
presentation window, replacing the current object completely. |
1215 |
|
1216 |
POPUP |
1217 |
Present the linked object in a non-persistent presentation |
1218 |
Murray & Quin [Page 20] |
1219 |
|
1220 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1221 |
window. That is, show the linked object while the user is |
1222 |
activating the link, and make it disappear when the user |
1223 |
releases activation. In the case that the popup is entered |
1224 |
without user activation, the user agent may provide a "Cancel" |
1225 |
button or another mechanism to make the popup window |
1226 |
disappear. |
1227 |
|
1228 |
SPLITSCREEN or HORSPLIT |
1229 |
Present the linked object in one pane of a horizontally split |
1230 |
window. |
1231 |
|
1232 |
ALONGSIDE or VERSPLIT |
1233 |
Present the linked object in one pane of a vertically split |
1234 |
window. |
1235 |
|
1236 |
7b. TARGET |
1237 |
Netscape Corporation have proposed to add a TARGET attribute to |
1238 |
the A element; its value is the name of the window in which to |
1239 |
display the result of following the link. |
1240 |
|
1241 |
This is most useful in conjunction with a mechanism (such as |
1242 |
FRAMES, not discussed in this document) to give names to windows. |
1243 |
However, if no window exists with the given name, a reasonable |
1244 |
action is to create such a window. |
1245 |
|
1246 |
An HTML client in a non-windowing environment would have to find |
1247 |
some way to indicate the presence of multuple active document areas, |
1248 |
and to allow navigation amongst them. |
1249 |
|
1250 |
7c. DINGBAT |
1251 |
The DINGBAT attribute, applied to the LINK element and the A |
1252 |
element, would be used to specify the entity name of a graphic |
1253 |
image (an icon) to associate with a hypertext link. The DINGBAT |
1254 |
attribute values must be specified by the HTML DTD as an SGML name |
1255 |
token group. |
1256 |
|
1257 |
When used with LINK, the icon may be used on an HTML user agent |
1258 |
toolbar. When used with A, the icon may be placed in close |
1259 |
proximity to the anchor's highlighted text, as a footnote marker |
1260 |
for example. |
1261 |
|
1262 |
There are advantages to using an entity rather than an external |
1263 |
graphic. Presumably, a user agent would pre-load the standard set |
1264 |
of entities, thereby eliminating the need to fetch a graphic |
1265 |
across the network. It is hoped that user agents will provide |
1266 |
users with a means to specify the system location of personalized |
1267 |
or customized versions of standard icons, thereby offering the |
1268 |
user the opportunity to exercise greater control over the user |
1269 |
interface and the graphical presentation. |
1270 |
|
1271 |
The DINGBAT attribute has already been proposed for lists and list |
1272 |
items in Dave Raggett's Internet Draft on HTML 3.0. User agent |
1273 |
behavior, in the face of contention between DINGBAT and SRC, must |
1274 |
be specified. |
1275 |
|
1276 |
7d. HILITE or HIGHLIGHT |
1277 |
Roy Fielding has pointed out that the author can |
1278 |
indicate a preference for the style of anchor |
1279 |
Murray & Quin [Page 21] |
1280 |
|
1281 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1282 |
highlighting. So far, the list of candidate |
1283 |
keywords are: |
1284 |
* None |
1285 |
* Button |
1286 |
* IconOnly |
1287 |
* Underline |
1288 |
* Outline |
1289 |
* Reverse |
1290 |
|
1291 |
7e. METHOD |
1292 |
From Ian Graham: It would often be convenient to |
1293 |
access a link using a defined HTTP method other than GET. For |
1294 |
example, suppose I have a LINK attribute defining a related, |
1295 |
searchable glossary. One desirable behavior is as follows: the |
1296 |
user highlights a word and clicks a mouse button (or presses a |
1297 |
glossary button). The browser accesses the linked object, passing |
1298 |
to it the highlighted text. The server then returns the glossary |
1299 |
entry relevant to the highlighted word. This requires |
1300 |
standardised methods and data encoding schemes. There is only one, |
1301 |
namely the HTTP TEXTSEARCH method, which is how ISINDEX search |
1302 |
queries are sent to a server. I therefore propose that the METHOD |
1303 |
attribute have two possible values, namely GET|TEXTSEARCH, to |
1304 |
indicate how the client should access the linked resource. |
1305 |
|
1306 |
7f. SRC |
1307 |
The SRC attribute, applied to the LINK element and the A element, |
1308 |
would be used to specify the location of a file containing a |
1309 |
graphic image (an icon) to associate with a hypertext link. When |
1310 |
used with LINK, the icon may be used on an HTML user agent |
1311 |
toolbar. When used with A, the icon may be placed in close |
1312 |
proximity to the anchor's highlighted text, as in the case of a |
1313 |
footnote marker for example. |
1314 |
|
1315 |
This extension of the applicability of the SRC attribute has |
1316 |
already been proposed for lists, list items, and admonishments in |
1317 |
Dave Raggett's Internet Draft on HTML 3.0. User agent behavior |
1318 |
remains to be specified in the face of contention between DINGBAT |
1319 |
and SRC attributes. |
1320 |
|
1321 |
7g. WHEN |
1322 |
Roy Fielding and Ian Graham have pointed out that user agents |
1323 |
currently exhibit different behavior between their processing of |
1324 |
hypertext links specified with the SRC attribute and those |
1325 |
specifiewd with HREF. Typically, user agents await user activation |
1326 |
before traversing a hypertext link specified with an HREF |
1327 |
attribute, while those specified with SRC are more often fetched |
1328 |
immediately. This distinction is a natural consequence of a |
1329 |
design which uses the SRC attribute to specify a hypertext link to |
1330 |
an embedded graphical image. |
1331 |
|
1332 |
The author can take advantage of an ability to specify when, or |
1333 |
the type of event, which should initiate the hypertext link. |
1334 |
|
1335 |
Roy Fielding suggested the following possible attribute values: |
1336 |
UserSelect as is the case for anchors and FORMS |
1337 |
AutoEntry as is the case for EMBED or IMG |
1338 |
AutoExit an interesting derivative |
1339 |
Export only used external to the user process |
1340 |
Murray & Quin [Page 22] |
1341 |
|
1342 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1343 |
|
1344 |
In response, Murray Maloney asked: Would the AutoExit derivative |
1345 |
provide a means for me to do indirection? For example, in |
1346 |
document A I have <A HREF=B#foo>, and in B I have <LINK NAME=foo |
1347 |
STYLE=AutoExit HREF=C>. Would asserting the anchor in A lead me |
1348 |
to C? If so, wonderful. If not, then why not and what then? |
1349 |
|
1350 |
Please explain the meaning of "Export"? That is, if I use it what |
1351 |
does it imply about "when should the action take place"? |
1352 |
|
1353 |
(Liam Quin things Export doesn't imply any action at all, but |
1354 |
doesn't yet understand why it might be useful) |
1355 |
|
1356 |
Consider these examples: |
1357 |
<LINK ACTION=POPUP WHEN=AutoEntry |
1358 |
REL=COPYRIGHT HREF="copyright.html"> |
1359 |
<A ACTION=POPUP WHEN=AutoEntry |
1360 |
REL=COPYRIGHT HREF="copyright.html"> |
1361 |
Copyright 1995 by Murray C. Maloney</A> |
1362 |
In either case, the user agent is expected to display the target |
1363 |
document in a popup as soon as the current document is retrieved. |
1364 |
|
1365 |
7h. OBSOLETES, UPDATES and DERIVED-FROM: |
1366 |
Roy Fielding also suggested the following relations: |
1367 |
OBSOLETES |
1368 |
when REL=OBSOLETES, the target document is a later version of |
1369 |
the current document; when REV=OBSOLETES, the target document |
1370 |
is obsoleted by the current document. |
1371 |
|
1372 |
UPDATES |
1373 |
When REL=UPDATES, the target document contains revisions to the |
1374 |
current document (would REVISES be clearer?). |
1375 |
|
1376 |
DERIVED-FROM |
1377 |
When REL=DERIVED-FROM, the target document was derived from the |
1378 |
current document; when REV=DERIVED-FROM, the current document |
1379 |
was derived from the target document, perhaps by automatic |
1380 |
processing or by manual editing. |
1381 |
|
1382 |
8. Acknowledgements |
1383 |
This paper is the synthesis and codification of ideas from |
1384 |
a variety of sources. It is only fitting that those who |
1385 |
have contributed to the discussion in various forums should |
1386 |
be acknowledged for their part in the recent attempt to |
1387 |
move this work forward. |
1388 |
Terry Allen, O'Reilly and Associates, terry@ora.com |
1389 |
Murray M. Altheim, NTTC, murray.altheim@nttc.edu |
1390 |
Brian Behlendorf, Indiana Univ., brian@organic.com |
1391 |
Bert Bos, Rijksuniversiteit Groningen, bert@let.rug.nl |
1392 |
Jon Bosak, Novell, Jon Bosak@novell.com |
1393 |
Henry Budgett, SCO, henryb@sco.com |
1394 |
Paul Burchard, burchard@geom.umn.edu |
1395 |
Dan Connolly, MIT/W3C, connolly@w3.org |
1396 |
Steve DeRose, Electronic Book Technologies, steve@ebt.com |
1397 |
Joe English, joe@trystero.art.com |
1398 |
Roy T. Fielding, Univ. of California (Irvine), fielding@ics.uci.edu |
1399 |
Peter Flynn, pflynn@curia.ucc.ie |
1400 |
Ian Graham, Univ. of Toronto, igraham@utirc.utoronto.ca |
1401 |
Murray & Quin [Page 23] |
1402 |
|
1403 |
INTERNET DRAFT Hypertext Links in HTML December 1995 |
1404 |
Dave Hollander, HP, dmh@hpsgml.fc.hp.com |
1405 |
Alex Hopmann, ResNova Software, Inc., hopmann@holonet.net |
1406 |
Craig Hubley, Craig Hubley & Associates, craig@passport.ca |
1407 |
Albert Lunde, Albert-Lunde@nwu.edu |
1408 |
Tom Magliery, NCSA, mag@ncsa.uiuc.edu |
1409 |
Eve Maler, ArborText, eve@doctools.com |
1410 |
Larry Masinter, Xerox, masinter@parc.xerox.com |
1411 |
Eric Miller, OCLC, emiller@oclc.org |
1412 |
Lou Montulli, Netscape Communications, montulli@netscape.com |
1413 |
David Morris, dwm@shell.portal.com |
1414 |
Dave Raggett, MIT/W3C, dsr@w3.org |
1415 |
Bob Stayton, SCO, bobs@sco.com |
1416 |
Stu Weibel, OCLC, weibel@oclc.org |
1417 |
Faith Zack, SCO, faithz@sco.com |
1418 |
|