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(_at_)contrext(_dot_)com 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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