If the pattern is chapter/title , then a node matches if it is selected by the expression root(.)//(chapter/title) , which selects all elements that are children of elements.
If the pattern is para[1] , then a node matches if it is selected by the expression root(.)//(para[1]) , which selects any element that is the first child of its parent.
If the pattern is id(‘S123’) , then a node matches if it is selected by the expression root(.)//(id(‘S123’)) , which is equivalent to the expression id(‘S123’) and selects the element with an ID value of S123 .