Kimber - HyTime and Arch Forms question

Subject: Re: HyTime and Arch Forms question
Date: 14 Sep 1997 00:00:00 GMT
From: "W. Eliot Kimber" <eliot@isogen.com>
Organization: ISOGEN International Corp.
Newsgroups: comp.text.sgml

Paul Madsen wrote:
>
> The HyTime standard allows a DTD element to inherit features and
> characteristics from an architectural form.

> Is the following legal?
>
> <!ELEMENT xref - O  EMPTY>
> <!ATTLIST xref
>                             idref        IDREF   #REQUIRED
>                             HyTime  NAME #REQUIRED >
>
> where I leave to the <xref> instance what type of HyTime architectural
> form it "belongs" to, e.g.

Yes.  Architectural mapping is validated for documents, not DTDs, so it
doesn't matter how the architectural mapping attribute gets set.  You
could also declare it as a name group if there is a fixed set of element
forms it could be derived from, or as an unfixed attribute with a a
specified (but changable) default value.

Note that in HyTime Second Edition, we explicitly account for the need
to have elements that are sometimes, but not always, links with the new
concept of "anchor constraints", which let you say that an element's
interpretation as a HyTime hyperlink is conditional on the actual
addressing of its anchors.  For example, the HTML A element, which is
only a link when the HREF attribute is used, can be declared like so:

<!ATTLIST A
   href     CDATA #IMPLIED
   HyTime   NAME  #FIXED "clink"
   anchcstr CDATA #FIXED "self cond"
   HyNames  CDATA #FIXED "linkend href"
>

The "anchcstr" attribute (anchor constraints) says that of the two
anchors of the clink, one is the anchor itself ("self") and the other is
a "conditional anchor", meaning that if that anchor is not addressed,
the element is not interpreted as a HyTime hyperlink (but is still
architectural, as though it had a form of "HyBrid").

If you have elements that will vary in their form based on context, I
would expect to use editor customizations to capture the context rules
and either hide the choice from authors or provide guidance in how to
make the choice.