I need to determine, for each <ref/> child, whether there is
  a <choice/> ancestor prior to the <define/> Ancestor.

prior?

In document order, in your example the define element is prior to the
choice. I suppose you are thinking in reverse document order, as you
mention the ancestor axis?

you can phrase your request more directly in XPath 2 draft, but using
xslt1 something like

<xsl:when test="ancestor::*[not(.//define)][self::choice]">
  I have a choice ancestor that doesn't have a define descendent

David


-- 
The LaTeX Companion
  http://www.awprofessional.com/bookstore/product.asp?isbn=0201362996
  http://www.amazon.co.uk/exec/obidos/tg/detail/-/0201362996/202-7257897-0619804


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