Problems with <draw:layer-set>

[Regina Henschel <regina.henschel@libreoffice.org>]

Hi all,

in ODF 1.2 we have

10.2.2 <draw:layer-set>
The <draw:layer-set> element defines a set of layers. If placed inside a 
<style:master-page> or <draw:page> element it defines a set of layers 
for that page. If placed inside the <office:master-styles> element it 
defines a set of layers for all pages that do not have their own set of 
layers.

So there exists three places, where an element <draw:layer-set> can 
occur. And from the last sentence I conclude, that inside a document 
there can be several <draw:layer-set> elements.

LibreOffice uses <draw:layer-set> only as child of 
<office:master-styles>. Calligra Karbon uses <draw:layer-set> as child 
of <draw:page>. Currently I investigate, how to make LibreOffice able to 
import a document, produced by Calligra Karbon.

Problems:

(A) Is it possible to have a <draw:layer-set> as child of a <draw:page> 
and at the same time a different <draw:layer-set> as child of that 
<style:master-page> to which the <draw:page> element refers? Or is there 
exactly one <draw:layer-set> to be used for a page: either its own, or 
that from its <style:master-page> or the default from <office:master-style>?

(B) Does a layer name need to be unique throughout the entire document? 
Or is it sufficient, if the name is unique in those one (or two, see 
problem A) <draw:layer-set> which is used for a page?

(C) May a layer name be the empty string? I come across this, because 
Calligra's UI allows it.



Additional problem in the ODF 1.2 spec:
19.189 draw:layer
The draw:layer attribute specifies the name of a layer in the layer-set 
of a document.

The wording "in the layer-set of a document" seems wrong to me, because 
there can exist several <draw:layer-set> elements in a document.

Kind regards
Regina