XML variable-access syntax

* ： children()
.Name ： child("Name")

@Name ： attribute("Name")
@* ： attributes()

..Name ： descendants("Name");
..@ ： retrieve a list of descendant attributes
..* ： retrieve every single nodes from a given element
..@* ： retrieve every single attributes defined both on an element and on all of its descendants.
..*.@* ： retrieve every single attributes defined on an element's descendants, but not on the elements itself.


p.s. parsing from right to left.