Hi Dean,
Out of the box, the role values that work are established by the global param 
named 'stylesheet.result.type', which is set in each stylesheet.  It is not set 
in the param.xsl file because it is an internal param that is not to be set by 
the user.  

- In fo/docbook.xsl, $stylehsheet.result.type is set to 'fo', so an imageobject 
with role="fo" is matched there.

- In html/docbook.xsl, the param is set to 'html'. Since chunk.xsl imports that 
file, it gets that value too.

- In xhtml/docbook.xsl and xhtml_1-1/docbook.xsl, it is set to 'xhtml', but the 
selection process will fall back to an imageobject with role="html" if there 
isn't an imageobject with role='xhtml'.  

- All the other stylesheets inherit the param value that they import.  Since 
htmlhelp imports html/docbook.xsl, it selects for 'html' too.  Same with 
eclipse and javahelp.  The epub stylesheet imports xhtml_1.1, it selects for 
'xhtml' (with fallback to 'html').

You mentioned role values of 'HTML', 'XHTML', 'fo-xep', and 'fo-fop'.  None of 
those would be recognized (it is case sensitive), and the selection process 
falls back to looking at image filename extensions to find one that is 
acceptable for the given output.

But you can override any of these by setting the param 
'preferred.mediaobject.role' in your customization layer to some value other 
than blank.  That param is checked first.  My example with 'fo-xep' set that 
param as an example of customizing the selection process.

Bob Stayton
Sagehill Enterprises
[email protected]


  ----- Original Message ----- 
  From: [email protected] 
  To: [email protected] 
  Sent: Monday, March 23, 2009 2:14 PM
  Subject: [docbook-apps] Imageobject choices for ROLE.


  Hello Docbookers,

  I have been moving some of my <graphic>'s over to <mediaobject>'s.  This is 
mainly to support SVG for FOP and PNG for HTML & XHTML. However, I was a bit 
baffled on the choice to use for MSHELP outputs. Are the choices for "role" for 
imageobject only "fop, HTML,XHTML, fo-xep, fo-fop"? 

  Obviously "role" can be anything, but I am specifically asking about the 
stock DocBook XSL processing when using these attributes. What is the 
stylesheets capable of?

  Thanks
  Dean Nelson

  PS: Most of the above info comes from Bob's book only, as I couldn't find any 
info on this in the XSL reference doc or in the TDG.


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