Element positions are not very intuitive, and not very reliable either, because they will change when you insert / delete elements.
This is very common in WS Security. Let us say you signing a UserNameToken which is at position 1, now after signing if you insert a X509token before the UserName token, the signature is no longer valid, because it refers to position 1.  We need to use the element names, not the positions.

Also ebXML needs to use a condition in their XPath expression, because they want to exclude from the signature, all header elements whose actor is nextMSH. That's why I included attribute based predicates, in the XPath subset.

Pratik




Thomas Roessler wrote:
On 2008-09-03 14:50:52 -0700, Pratik Datta wrote:

  
Unfortunately XPath is become very complicated. XPath 2.0 is even
more complicated. What we need is something simple - basically I
am trying to define an XPath 0.5 , where we can use the simple
slash notation of XPath, and not have to support all the complex
features.
    

how about this?

http://www.w3.org/TR/xptr-element/