Iteration position and size

The spec says:

  In the context of a p:for-each or a p:viewport, the
  p:iteration-position function reports the position of the document
  being processed in the sequence of documents that will be processed.
  In the context of other standard XProc compound steps, it returns 1.

But test viewport-005 checks the position inside a p:choose where we
clearly expect the value not to be reset. For which other steps do we
expect the value not to be changed? try/catch? group? 

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The bane of my existence is doing
http://nwalsh.com/            | things that I know the computer could
                              | do for me.--Dan Connolly