Re: [xml-dev] Beware of XPath expressions that produce false positives

[David Carlisle <d.p.carlisle@gmail.com>]

On 24 September 2016 at 22:02, Costello, Roger L. <costello@mitre.org> wrote:

David Carlisle wrote:

Also you are classing attributes as non-empty content
but not namespace nodes so

<B foo=""/> is non empty but
<B xmlns:x="data:,hello"></B> is empty

Ah, good catch David.

Okay, I added namespace::* to the XPath that David provided, to take into account namespaces. Here is the new XPath: empty((node(),@*,namespace::*))

 

Here are the results I got from running my XSLT program using the new XPath:

 

	Is empty?
<B/>	true
<B></B>	true
<B>&null;</B>	true
<B>  </B>	false
<B><!-- Hello, world --></B>	false
<B><bad/></B>	false
<B>99</B>	false
<B x="10"/>	false
<B xmlns:b="test"/>	false

 

Perfect!

 

Those results are from running SAXON in Oxygen XML.

 

John and David pointed out I might get different results with another parser. Specifically, another parser might discard comments and the whitespace in <B>  </B>. Such a parser would produce these results:

or more likely the same parser, differently configured, for  example if you have xsl:strip-space elements="*" in the xslt, or if you call saxon with -strip option or with a DTD or schema that specifies that B takes element content or....

 

 

	Is empty?
<B/>	true
<B></B>	true
<B>&null;</B>	true
<B>  </B>	true
<B><!-- Hello, world --></B>	true
<B><bad/></B>	false
<B>99</B>	false
<B x="10"/>	false
<B xmlns:b="test"/>	false

 

Is there any way to write an XPath expression that always produces the results shown in the first table, regardless of which parser is used?

No if a previous part of the pipeline has removed white space then <b> </b> _is_  <b/>

 

 

/Roger

 

David