xpath /descendant-or-self - Searching for a node in a particular tree

[wetip1]

I am reading about the short-cut, '//', which apparently is a shortcut for:'/descendant-or-self'it is clear what to expect, say, from a simple example of such an expression, eg, //myNodeIt will return a node list of all instances in the document, found from the root, of elements called 'myNode'. However, what is the meaning of a more complicated expression, such as://aNode//myNode?Since // (being the shortcut for '/descendant-or-self') matches the root node twice, does this mean the first part of the expression '//aNode' is redundant, and only adds to the time it takes to complete the execution of the expression (after having still only found all expressions throughout the whole document, of 'myNode') ? Are '//myNode' and '//aNode//myNode' going to result in exactly the same thing? Finally, if I was searching through the document for an instance of node 'myNode' which was an indirect descendant of node 'interestingTree'. But I don't want the instance of node 'myNode' which is an indirect descendant of node 'nonInterestingTree', how should I do this ? for example, searching in the document:\[code\]<root> <anode> <interestingTree> <unknownTree> <myNode/><!-- I want to find this one, not the other, where I don't know the path indicated by 'unknownTree' --> </unknownTree> </interestingTree> <nonInterestingTree> <unknownTree> <myNode/> </unknownTree> </nonInterestingTree> </anode> <anode> <someOtherNode/> </anode></root>\[/code\]Thanks!