Re: Attribute encryption & Blair's message

RE: Attribute encryption, Schema validation, role of XSLT, scope of XML Encryption document>Simply ignoring everything you don't understand in an element, while assuming the rest is something you do understand, seems >incredibly brittle and error prone. 
Thane, my example deals with a scenario where a intermediate party needs to look at specific components of a document, eg, it may need information to route the document.  The intermediate party looks for specific elements only (using say, Xpath), and does not need to examine the other data (payload).  Could you explain why this kind of code would be brittle or error-prone ?