[xmlroff] DocBook to PDF with xmlroff

[Tim W. <tw...@re...>]

So I managed to get a DocBook document converted to PDF using xmlroff
and the libfo-compat.xsl stylesheet (with the two modifications I
posted) applied to docbook-xsl output, and I'm really impressed.

The two immediately obvious things missing are:

* PNG graphics (@background-image)
* @white-space-treatment="preserve" for DocBook <screen> nodes

The only other thing wrong with the output for this document is that
an <orderedlist> comes out as a weird array of dots instead of any
text.  I haven't been able to make a smaller test case yet.

What steps are needed to add @background-image and
@white-space-treatment support?

Tim.
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