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Subject: Re: DOCBOOK-APPS: Re: conditionalization of XML

Daniel Veillard <veillard@redhat.com>:
>   Now to be relatively specific about <?if?> as much as I can since I
> don't have any clear picture of how the selection is actually done, it seems
> to be in the line of the previously found standard extention abuses
> like #pragma foobar for Winblows C compilers or various custom PI
> that each SGML toolchains seems to have developped to tie in their 
> customers in the 90's (I may get some heat for this, I don't care ;-)

You know, there's reason people keep re-inventing mechanisms for this.
It's because they need to get work done -- and getting work done often 
means wanting to conditionalize documents without spending days on some
elaborate custom XSLT hack.

> I would really prefer to get DocBook fixed to allow proper conditionalization
> at the *markup* level (if the current solution is not sufficient for
> users' needs like Eric), which then will be close to trivial to handle 
> correctly in the existing XSLT tools, independantly of the toolchain used.

Norm?  Are you listening?  Is this anything that the DocBook development
group is thinking about?

>   Now if a number of people did voice in saying that's the kind of processing
> they really need, that there is a clean and public description with
> review of the suggested extension, then I would certainly be an early
> implementor of said feature.

   Attribute/value  pairs  from  the  command  line  are  matched
   against  the  attributes  associated  with  certain processing
   instructions  in the document. The instructions are <?if?> and
   its inverse <?if not?>, <?elif?> and its inverse <?elif not?>,
   <?else?>, and <?fi?>.

   Argument/value  pairs  given  on  the command line are checked
   against   the   value   of  corresponding  attributes  in  the
   conditional  processing  instructions.  An  `attribute  match'
   happens  if  an  attribute  occurs  in  both  the command-line
   arguments  and  the  tag,  and the values match. An `attribute
   mismatch'   happens   if  an  attribute  occurs  in  both  the
   command-line  arguments  and  the  tag,  but the values do not

   Spans  between  <?if?>  or  <?elif?>  and the next conditional
   processing  instruction  at  the same nesting level are passed
   through unaltered if there is at least one attribute match and
   no  attribute  mismatch;  spans  between <?if not?> and <?elif
   not?>  and  the  next  conditional  processing instruction are
   passed   otherwise.   Spans  between  <?else?>  and  the  next
   conditional-processing  tag  are  passed  through  only  if no
   previous  span  at  the  same  level  has been passed through.
   <?if?>  and  <?fi?>  (and  their  `not'  variants)  change the
   current nesting level; <?else?> and <?elif?> do not.

   All  these  processing  instructions  will be removed from the
   output  produced. Aside from the conditionalization, all other
   input  is  passed  through  untouched;  in  particular, entity
   references are not resolved.

   Value  matching  is  by string equality, except that "|" in an
   attribute  value  is  interpreted as an alternation character.
   Thus,  saying  foo='red|blue'  on  the  command  line  enables
   conditions  red  and blue. Saying color='black|white' in a tag
   matches     command-line    conditions    color='black'    and

   Here is an example:
Always issue this text.
<?if condition='html'?>
Issue this text if 'condition=html' is given on the command line.
<?elif condition='pdf|ps'?>
Issue this text if 'condition=pdf' or 'condition=ps'
is given on the command line.
Otherwise issue this text.
Always issue this text.

		<a href="http://www.tuxedo.org/~esr/";>Eric S. Raymond</a>

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