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Re: [xsl] seriously trivial question about processing the root element - not at all trivial
Subject: Re: [xsl] seriously trivial question about processing the root element - not at all trivial|
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 19 Mar 2003 21:24:26 -0500
At 2003-03-19 17:16 -0500, Robert P. J. Day wrote:
more than one book i've been reading has presented examples
of processing an XML document whose document element is, say,
....etc etc ...
if one assumes that an XML document will have a single
document element anyway, is there any value to the template
that matches "/", if one is going to start processing at
the document root anyway?
Absolutely yes there is value.
at least in the above example, it seems to be little
more than aesthetics. is this accurate?
Not at all from my perspective ... I believe much more than aesthetics are
Actually, I counsel the students of my training courses to do the above
because it "protects" a stylesheet from abuse.
From XSLT's perspective, *every* stylesheet will work with *every* source
file ... where "work" is loosely defined as "produce a well-formed result
from the given inputs".
Consider that I have a business card stylesheet that skips over the
document element <card> and just relies on the built-in templates to get to
the template rules for <name> and <address>.
Should I accidentally or maliciously pass an invoice instance to the
business card stylesheet, the built-in template rules might easily find
<name> and <address> under <buyer> and nicely format my invoice instance as
a business card ... accurate but nonsensical results.
However, with a root template rule that pushes the <card> child, a passed
<invoice> instance will produce an empty result: this is not a well-formed
instance (though it happens to be a well-formed external parsed general
entity) and would appropriately choke the next step of a multi-step
transformation as a document entity, or at least would easily be recognized
as the result of improper use of the stylesheet.
So far, so good ... but what if I pass a greeting card instance with a
<card> document element to the stylesheet? That would also produce
nonsensical results. At this point I support my argument to my students
that "namespaces are good, not evil" and show the students how:
Would be the *best* protection from a business card stylesheet being abused
by being passed an unexpected source document that might kick in the
built-in rules to produce a non-empty but nonsensical result.
So I personally consider such a practice as a "good" practice. And it
supports my namespace preaching. It is not at all a trivial practice from
I hope this helps.
Upcoming hands-on in-depth XSLT/XPath and/or XSL-FO
North America: June 16-20, 2003
G. Ken Holman mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
Crane Softwrights Ltd. http://www.CraneSoftwrights.com/s/
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