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Date: Wed, 04 Aug 1999 14:53:41 -0500
From: Dan Connolly <connolly@w3.org>
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Subject: Re: Safe use of Meta Tags
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Eliot Christian wrote:
> It is common to find several ways of representing very similar
> concepts in HTML Meta Tags. Yet, metadata authors may wish to
> assert that various tags ought to be considered equivalent for
> search purposes.
> Toward this goal, some of us are trying out a mechanism where
> an additional attribute is provided within the Meta element.
> The attribute is a "Z" number (corresponding to registered
> concepts in the Z39.50 Bib-1 Attribute Set, Use Attributes).
> We are putting the Z attribute as the last part of a Meta
> element, in the hope that it will be safely ignored by
> processors that don't understand what it is. For example,
> <head>
> <title>My Very Own Web Page</title>
> <meta NAME=3D"GILS.Originator" CONTENT=3D"U.S. Geological Survey" z=3D"=
> <link REL=3D"schema.GILS"      HREF=3D"elements.html#table_1">
> <meta NAME=3D"AUTHOR"          CONTENT=3D"Eliot Christian" z=3D"1005">
> <meta NAME=3D"dc.creator"      CONTENT=3D"Eliot Christian" z=3D"1002">
> <link REL=3D"schema.dc"        HREF=3D"http://purl.oclc.org/metadata/dc=
> </head>
> Is this safe?

sort of. It doesn't conform to any W3C specs, but most software
will "safe"ly ignore it. But you're not guaranteed that somebody
else isn't using the same syntax with different semantics.

If you want that guarantee, use XML namespaces; i.e.

<head xmlns:z=3D"http://lcweb.loc.gov/z3950/-or-some-such">
<title>My Very Own Web Page</title>
<meta NAME=3D"GILS.Originator" CONTENT=3D"U.S. Geological Survey"
	z:Bib-1=3D"1005" />
<link REL=3D"schema.GILS"      HREF=3D"elements.html#table_1" />
<meta NAME=3D"AUTHOR"          CONTENT=3D"Eliot Christian"
	z:Bib-1=3D"1005" />
<meta NAME=3D"dc.creator"      CONTENT=3D"Eliot Christian"
	z:Bib-1=3D"1002" />
<link REL=3D"schema.dc"        HREF=3D"http://purl.oclc.org/metadata/dc/"=

and describe what this syntax means at

Note the /> at the end of the meta tags, to conform with XML.

For details, see:

XHTML=99 1.0: The Extensible HyperText Markup Language
     A Reformulation of HTML 4.0 in XML 1.0
W3C Working Draft 5th May 1999

especially section 3.1.2 "Using XHTML with other namespaces"

Dan Connolly, W3C