another question for the xpath query

[Wei Cheng <We...@baylor.edu>]

Hi, Gary:
   I have used
   /doc/name[firstname=following-sibling::name/firstname]/firstname
   to get the primary key nodelist what I want.
   if the nodelist's length is 0 then is primary key ,else fale.
   Thanks for your advice!
   I still had some questions about this expression,
   It seems to me
   firstname=following-sibling::name/firstname returns a boolean
   value,
   What does /doc/name[true]/firstname and  /doc/name[false]/firstname
   mean? Can you explain this to me?
   I not only want to get the result, but I want to know why.
   Thanks!
   Wei Cheng