dbfo / example

Hi there,

  I am looking at the documentation of example at:

http://www.docbook.org/tdg/en/html/example.html

  I cannot tell from this page, that this particular docbook element
supports the <?dbfo pgwide="1"?> processing instruction.

  Am I reading this page incorrectly ? Where is the list of processing
instructions supported for a particular docbook element ?

Thanks !
-- 
Mathieu