Abel,
At 04:07 PM 6/18/2007, you wrote:
I'm not sure if I get this right, so I'm asking here. If I have the
following two rules:
<xsl:template match="/root" />
<xsl:template match="/*" />
I receive an "ambiguous rule match" error if the input matches the
first. I figured, '*' is not very selective, so it should've
conceived lowest priority (I know that a single '*' has prio -.5).
What I'd guess is that I am having a compound rule here, similar to
'node/child' or 'node/*' which both receive prio +.5, with the
parent node being the document node. Am I correct?
Yes. Both of these fall into the "anything else" category. There are
three categories:
1. Simple tests by name, on the child or attribute axis in a single step
e.g. "root" or "@root" -- priority 0
2. "Wildcard" matches on the child or attribute axis in a single step
e.g. "@*" or "comment()" -- priority -0.5
3. Anything else
e.g. "//root", "/root", "/*/root" or "/*" -- priority 0.5
(There's also a category between rules 1 and 2: a match on a
namespace-and-type, with a single step, such as "html:*" or
"svg:node()", gets priority 0.25.)
Or should a processor distinguish and select the first as having a
higher prio (which intuitively seems more correct)?
Early drafts of XSLT attempted to specify such a cascade, but either
it proved difficult to specify completely, or it appeared unlikely to
work transparently enough, so the rules were simplified.
This does mean that you can get edge cases like yours, where matches
using wildcards (node tests by type, that is, as opposed to those by
name) fall into the "anything else" category by virtue of extra steps
in the XPath.
Of course I can use priority='x', but I'm curious about the default prio here.
Given the rough granularity of the discriminations, it's generally
wise to make priorities explicit as soon as there's any reasonable
chance for confusion.
Cheers,
Wendell
PS: the same happens when I over-specify the first rule, i.e.:
/root[foo[bar='y']]
Yes, that's also an "anything else".
======================================================================
Wendell Piez
mailto:wapiez(_at_)mulberrytech(_dot_)com
Mulberry Technologies, Inc. http://www.mulberrytech.com
17 West Jefferson Street Direct Phone: 301/315-9635
Suite 207 Phone: 301/315-9631
Rockville, MD 20850 Fax: 301/315-8285
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