Re: [xsl] Best Way to Break Up Nested Structures Based On Inline Elements

["Imsieke, Gerrit, le-tex gerrit.imsieke@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Eliot,

I think this can be tackled with what I call "upward projection", see 
for ex. https://markmail.org/message/kmq2g4fidmw6cofz

You'd identify all leaf elements and group them (maybe a combination of 
group-starting-with="two-colum-start" and 
group-ending-with="two-colum-end" is in order here).

Then for each group you transform the top-level block in a certain mode, 
with a tunneled parameter. The tunneled parameter contains the current 
group and its ancestors.

In the template that matches any element in this mode, you check whether 
the tunneled parameter contains the current element. If so, the 
next-match identity template will apply, if not, nothing will be written 
to the result.

There's a special template in this mode that matches the 
two-column-start element. It will create <fo:block span="none"> and then 
go on processing the children.

I'm not 100% sure whether this works, but I have an intercontinental 
flight ahead of me. It will give me some time to create working code, 
unless you're faster implementing the suggested solution (or a better one).

I guess that the solution scales with the number of splitting points 
times the number of leaves, so performance may deteriorate for large 
documents with frequently changing column spans.

Gerrit

On 18/04/2018 19:45, Eliot Kimber ekimber@xxxxxxxxxxxx wrote:
> Using XSLT 2 with Saxon.
>
> In the context of generating XSL-FO markup where there tree of fo:block elements can be quite deep, I need to break the blocks into a sequence of top-level blocks that specify @span based on the presence of markers anywhere in the heirarchy. This is to support FOP's strict implementation of the FO spec, which only allows specifying column spans on direct children of fo:flow.
>
> In my processing I'm emitting marker elements to signal the starts and ends of areas that need to change the column spanning, e.g.:
>
> <fo:block span="all">
>    <fo:block>
>       <fo:block>
>         <fo:block>
>            <two-column-start/>
>        </fo:block>
>        ...
>       <two-column-end/>
>     </fo:block>
>    <fo:block>...
>    </fo:block>
> </fo:block>
>
> Where the result needs to be:
>
> <fo:block span="all">
>     <!-- Stuff before two-column start -->
> </fo:block>
> <fo:block span="none">
>     <!-- Stuff up to <two-column-end/> marker -->
> </fo:block>
> <fo:block span="all">
>    <!-- Stuff after <two-column-end> marker -->
> </fo:block>
>
> There must be a general pattern for solving this kind of transformation pattern but I'm not seeing it or not remembering it.
>
> I can think of a recursive algorithm to do it but is there a simpler or more efficient approach? Conceptually it's a for-each-group problem but the structure of the content doesn't see to lend itself to grouping.
>
> Thanks,
>
> Eliot
> --
> Eliot Kimber
> http://contrext.com
>   

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