Re: [xsl] Re: XPath to select node according to xml:lang attribute

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Hi,

On 4/15/2011 2:22 PM, Chris wrote:
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> On 04/15/2011 02:18 PM, Philipp Kursawe wrote:
> > Hmm I cannot use XSLT in my context. I can only use XPath. So I guess
> > I would have to select "en-us" first and see if there is a result, if
> > not select "en" and so on. Or could I "||" chain multiple XPath
> > selects?
> > //text[@id='color' and lang('en-us')] || //text[@id='color' and
> > lang('en')] || //text[@id='color']
>
> Not sure what your context is...  You canbt put the || in an XPath, but
> if youbre in some procedural language like Perl or Java, then yes.
> Pseudocode:
>
> color_label = select( "//text[@id='color' and lang('en-us')]" ) ||
>                select( "//text[@id='color' and lang('en')]" ) ||
>                select( "//text[@id='color']" )
>
> That would (presuming normal behavior of logical or) get the best match
> for you.

Keep in mind, however, that what we have in XPath 1.0 "|" is a union 
operation, not an "or". So,

//text[@id='color' and lang('en-us')] |
//text[@id='color' and lang('en')] |
//text[@id='color']

will get us all the nodes in //text that have @id='color', irrespective 
of their lang() value, because the third term in the union collects them.

To do a cascading conditional like this in XPath 1.0 alone generally 
requires building conditionals into the predicates, as in

//text[@id='color'][
  @xml:lang='en-us' or
  (@xml:lang='en' and not(../@xml:lang='en-us') or
  not(../@xml:lang='en-us' or../@xml:lang='en')] ]

where the fallback cases (the second and third operands of the boolean 
'or' here) are excluded by filtering themselves out when the preferred 
cases are available.

Here the attribute values are tested directly since the lang() function 
works only on the context node, and we have to test the siblings. (So we 
have to do without the case-insensitive test built into lang().)

This is easier in XPath 2.0, where we can do something like

//text[@id='color]/(.[lang('en-us')],.[lang('en')],.)[1]

Cheers,
Wendell

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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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