Hi,



At 06:00 AM 8/4/2008, you wrote:
2008/8/2 Michael Kay <mike@xxxxxxxxxxxx>:

>> Out of interest, does xml:lang annotate the input tree, or does the

>> lang() function walk the ancestor axis behind the scenes?  Or

>> is it all implementation dependent?

>

> It's implementation-dependent, of course.

>

> Saxon walks the ancestor axis when you use the lang() function. I 
think it's

> used too rarely to be worth optimizing.



So (for Saxon anyway) doing:



test="lang('foo', .)"



is pretty much the same as:



test="ancestor-or-self::*/@xml:lang = 'foo'"

Or slightly more exactly, ancestor-or-self::*[@xml:lang]/@xml:lang = 'foo'



except that the lang() function should return true if the lang tested
is a subset of that declared in the attribute.

... and also the test is case-insensitive, in accordance with IETF 
RFC 3066 (http://www.ietf.org/rfc/rfc3066.txt), referenced by 
xml:lang (http://www.w3.org/TR/REC-xml/ section 2.12). So the 
xml:lang values of 'EN-GB', 'en-us' and 'en' all test true to lang()='en'.



So given an existing proprietary solution that walks the ancestor axis
a lot, you're not going to gain anything by switching to xml:lang...

I submit that speculating on performance differences vs alternatives 
is somewhat pointless, since it will depend on the implementation. 
It's not that it couldn't be optimized (especially if it were 
supported in the parser), so much as that it might not be.



Cheers,
Wendell


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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