[xslt] Adding support for variable reference inside user-defined function that is used in xsl:key definition

[Jirka Kosek <jirka kosek cz>]

Hi libxslt developers,

Daniel suggested me to open this issue once again now on this mailing list.

I have implemeted internationalized indexing feature as a part of the 
DocBook XSL stylesheets. With internationalized indexing you can get 
proper grouped and sorted index for languages like German, French, 
Czech, Spanish and many others. In a near future support for CJKV 
languages is planned.

Unfortunately XSLT 1.0 is too powerless for this task. My solution is 
depending on several EXSLT features. One of them is user defined 
function that is used in a definition of xsl:key. The problem is that 
this function must reference global variable in its body.

As I understand Daniel's opinion is that this is error because XSLT 1.0 
spec forbids reference to variables inside expression used in xsl:key 
definition (use attribute). My opinion is that this does not say 
anything about usage of variables inside functions that are used in 
xsl:key. This feature is a part of EXSLT and it is not covered by XSLT 
spec anymore IMHO.

The problem is that relation of EXSLT to XSLT 1.0 is not 100% clear and 
it is then hard to decide where the truth is.

I can support my point of view by fact that both Xalan and Saxon allow 
usage of variable refence in this particular situation.

You can find previous discussion in comments for the following bug:

http://bugzilla.gnome.org/show_bug.cgi?id=122483

Usage of user-defined function that references global variable in 
xsl:key is essential for internationalized indexing because xsl:key is 
needed for grouping which is done by Muenchian method. I tryed to use 
different grouping method that does not rely on xsl:key. I was 
successful -- new implementation worked in xsltproc. But it was 40 
(forty) times slower than xsl:key based implementation performed by 
Saxon or Xalan. You can imagine how many people will use tool that needs 
several minutes to process medium sized document.

Do you think that you might change behaviour of libxslt in order to 
support variable references inside user-defined functions that are used 
in xsl:key? I think that now it is clear that there is a real demand for 
this feature at least from DocBook users who need indexes in non-English 
languages.

					Jirka

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