[Xmlgraphics-fop Wiki] Update of "WhitespaceManagement" by JeremiasMaerki

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The following page has been changed by JeremiasMaerki:
http://wiki.apache.org/xmlgraphics-fop/WhitespaceManagement

The comment on the change is:
Some thoughts...

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  When the Renderer encounters a fox:best-fit element it analyses the available space in BPD within the current page and selects the alternative which fits "best" within the remaining BPD. By best fit, I mean the BPD of the alternative is less than remaining BPD but more than the BPD of all other alternatives which are less than the remaining BPD.
  
+ == Questions ==
+ 
+  * I know that in this particular requirement such an alternative block will not be broken across pages. But since the XSL working group has it on their requirements list, is it thinkable that those block need to be broken across pages?
+ 
+  * Are there better suited names for the new elements?
+ 
+    * fox:best-fit-block and fox:best-fit-alternative perhaps? "alternative" seems somewhat too generic. "best-fit-block" stresses that this is about block-progression-direction only.
+ 
+ == Thoughts for a possible implementation ==
+ 
+ First thought is to implement it similarly to a block-container with stretch and shrink. The implementation could measure the min/opt/max of every alternative and could calculate a combined min/opt/max from that. Creating Knuth elements for this combined min/opt/max is easy (a single box plus glue for the whole best-fit block with no break opportunity in between). After the page breaking, generating the contents of a particular alternative is easy and can be done the same way as for block-container.
+ 
+ What's critical is the optimum BPD for the whole block. Assuming you are creating a catalog with each article starting with the same larger structure. After that you have some variable length content. Since the first block always takes some space you will want to keep it together. This can lead to larger white areas on a page after the end of an article. You may be able to fill that with additional content, an additional picture perhaps. But that should only happen if there's really room to waste. So in this case the optimum value is 0pt. Maybe each alternative would have to have an id attribute and the best-fit block will contain a reference to the preferred alternative. The preferred alternative's optimum height will then become the best-fit block's optimum height. In the case where you don't want any additional content in the normal case, you'd specify an empty alternative and assign its id to the best-fit block.
+ 

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