"> ]> DocZilla Examples Linking DocZilla currently supports the following hypertext links: ID/IDREF(S), HyTime clinks with nameloc, treeloc and queryloc (URL notation), XLinks and IDLoc XPointer and HTML Anchors. Examples are given in this section. You will note that following a link highlights the target. You can turn this off by setting an environment variable "MDE_DO_NOT_SELECT_LINK_TARGET" to non-empty value, e.g. "1". In Windows NT/2000/XP you can do thisb in the control panel. In Windows 95/98/ME you must modify the autoexec.bat file. If you are using Linux consult the manual page of your shell on how to set environment variables. Link Destinations Link destinations in both XML or SGML documents can be identified by associating an ID type of attribute value with an element - any element (provided the Document Type Definition has allowed it for the element). The following example of a chapter identified as a potential destination with an ID value of "ChapterIX":
<chapter id="ChapterIX"> ... </chapter>
The reader should take care to observe the "id" in the above example is the attribute name - not its type. It is the type of the attribute which must be declared to an "ID" for the attribute to be recognized as a link destination. The only way the parser can know that an attribute value is of an ID type is by reading the attribute definition for the element. For an SGML document or an XML documents with a DTD this information will be gotten by DocZilla from the DTD. In the case of an XML document without a DTD it is possible to declare ID attributes in the internal subset without having a full DTD or even element definitions. For example:
<!DOCTYPE book [ <!ATTLIST chapter id ID #IMPLIED> ]>
is sufficient to enable the parser to recognize the id attribute on chapter elements as ID types. IDREF Links This entire paragraph is an example of an IDREF to ID Link. An attribute declared to be an IDREF type has a value of "dest1". When you click anywhere on this paragraph you will jump to element which has an attribute of type ID with a value of "dest1". Go ahead and do this now. The markup for the para element above with the IDREF attribute to "dest1" looks like this:
<para idref="dest1">This ... now.</para>
Like ID attributes, IDREF attributes must be declared in an attribute definition to be recognized as link sources. Here is an example of attribute definition for para with an IDREF declaration:
<!ATTLIST para idref IDREF #IMPLIED>
The style of the link source paragraph above (red text, underlined, pointer-type cursor) is accomplished with a Cascading Style Sheet (CSS) Level 2 rule with a selector for the attribute idref. The following rule causes any element with an attribute named idref to be so styled:
*[idref] { text-decoration: underline; color: blue; cursor: pointer; }
IDREF links can not be used to link to URLs or external files. Many validating SGML or XML parsers will report when an IDREF does not have a matching ID in a file. DocZilla simply ignores IDREF links which cannot be resolved. IDREF links always are "replace": that is, the current browser window is positioned over the link target, replacing the link source position. HyTime NAMELOC Links Named Locations provide redirection of link targets. IDREFs point at the ID of a Named Location (NAMELOC) which contains the ultimate target of the link in an NMLIST. The NAMELOC can occur anywhere in the document. It is possible to used Named Locations to group all link destinations in one place in the document where link targets can be easily maintained. Another advantage of NAMELOC is that NMLISTs can refer to external files. Perhaps the most important advantage of NAMELOC is that can be used to implement out-of-line links where link targets are kept in an external intermediary document, for example, where a CD-ROM program refers to a file on the Web for the most up-to-date Web-based links. NAMELOC is from HyTime, an ISO standard related to SGML. HyTime clinks with ENTITY type linkends Here is a HyTime clink whose linkend attribute type is ENTITY and the target document is target.sgm Here is a HyTime clink whose linkend attribute type is ENTITY and the target is target.sgm. Note that the system identifier for this entity contains XPointer IDLoc (shorthand notation) so we will scroll to id1 in the target document. Internal HyTime clinks with nameloc Here is a link to id1. Here is a link to id1 id1 via nameloc. Here is a link to id1 nameloc1 via 2 namelocs (nameloc4 -> nameloc1). External HyTime clinks with nameloc Here is a link to target.sgm target Here is a link to id1 in target.sgm id1 . Here is a link to middle.sgm nameloc1 nameloc1 from where we jump to somewhere else. After you try this once, you can edit the middle.sgm file so that the the location points to file target2.sgm. Once you do that change, this link here will go to another location than it initially did. This simulates the situation where this document sits on a CD-ROM for example, but you can still change where the link points to. Internal HyTime clinks with treeloc - linking to elements without an ID Here is a link that first locates element with ID doc1 (the root element), then the second child of that (chapter) and the second child of that (sect1) and the first child of it (para) which begins "DocZilla currently supports". 1 2 2 2 HyTime queryloc HyTime queryloc lets you employ non-HyTime links. First, you define a NOTATION for the link type. Then you must have a module that understands your notation and plug that into the HyTime engine. DocZilla will have such a pluggable interface for third-party developers to create their own queryloc handlers. Currently we have tested this and created a notation handler for the HTML URL type link. With the help of HyNames attribute renamer attribute and queryloc we created an element called "a" whose usage is exactly like the HTML A element. Here is a HyTime queryloc clink using URL notation to id2. Here is a HyTime queryloc clink using URL notation to target.sgm. Here is a HyTime queryloc clink using URL notation to DocZilla web page. Simple XLink Here is a simple XLink to DocZilla web site. Inter-document Link Targets id1 . . . . . id2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some targets Congratulations - you've reached the first link destination. The markup for this paragraph looks like this:
<para id="dest1">Congratulations ... this:</para>
Click here to go back to the section on IDREF to ID links.