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   Re: Using ID's usefully ?

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  • From: "John E. Simpson" <simpson@polaris.net>
  • To: xml-dev@ic.ac.uk
  • Date: Fri, 21 May 1999 00:18:01 -0400

At 07:57 PM 05/20/1999 -0700, Winton Davies wrote:
>...I hope the problem is clear: Principled re-use of ID's, and 

I didn't really understand what you were trying to do. But now seems
perfectly natural to me to use attributes for IDs, although I was confused
about them myself at first. As I've come to understand it, an ID doesn't
uniquely identify content (that is, the "thing" that the document
represents). It uniquely identifies an occurrence of an *element* (that is,
a piece of the markup).

>It seems strange the only way to use IDREF's 
>is in attributes (especially as there is no default "value" (c.f "id" 
>for ID) ATTRIBUTE, nor a way to specify the ELEMENT TYPE of IDREF one 
>may have).

The idea of a default value for an ID attribute is attractive to me; my DTD
specifies numerous elements that can occur only once in the tree, and I
wanted to declare defaults for all of these. When I raised the "Why not?"
question on xml-dev a few months back, it was conceded that in a case like
this, defaults might be useful, but the general feeling was that this
wasn't a typical case. The point was moot anyhow: XML 1.0 just doesn't
allow it.

>Also - how does one specify multiply IDREFS ? <tag attr1="1" 
>attr1="2"> or something else ?

Separate them with spaces: <tag attr1="1 2">

John E. Simpson            | The secret of eternal youth
simpson@polaris.net        | is arrested development.
http://www.flixml.org      |  -- Alice Roosevelt Longworth

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