XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (375 page)

• Variants on the
  /
  operator that can be used to write abbreviated path expressions, notably
  /
  as a freestanding expression,
  /
  at the start of a path expression, and the
  //
  pseudo-operator.
  
• What I call the Venn operators:
  union
  ,
  intersect
  , and
  except
  . These are often used to combine the results of several path expressions, or to form a step of a path expression.
  

Examples of Path Expressions

Before describing the different kinds of path expression in more detail, it may be helpful to look at some examples.

Expression	Description
para	Selects all the element children of the context node.
@title	Selects all the title attributes of the context node. The result will either be empty or contain a single attribute node.
book/author/first-name	Selects the elements that are children of the elements that are children of the elements that are children of the context node.
para[@id]	Selects all the element children of the context node that have an id attribute.
para/@id	Selects the id attributes of all the element children of the context node. This differs from the previous example in that the result is a sequence of attribute nodes rather than a sequence of element nodes.
/*/para	Selects all the element children of the containing document element (that is, of the outermost element of the document containing the context node). The * is a wildcard that selects all elements on the chosen axis.
$sections/body	Selects all element children of nodes in the sequence identified by the variable $sections . A type error occurs if $sections contains an item that isn't a node. The results will be in document order even if the original sequence $sections isn't in document order.
$sections[3]/body	Selects all element children of the third node in the sequence identified by the variable $sections .
$sections/ .	Selects all the nodes that are present in the value of the variable $sections , but with duplicates removed, and sorted into document order. The only effect of the /. in this case is to force the reordering and deduplication.
/contract/clause[3]/subclause[2]	Selects the second of the third of the that is the document element. If the document element is not a , or if any of the other components are missing, it produces an empty sequence.
//figure	Selects all the elements in the document.
city[not(@name = preceding-sibling::city/@name)]	Selects all the child elements of the context node that do not have a name attribute that is the same as the name attribute of a preceding element with the same parent. It thus selects a set of child elements with unique names.
*/name()	Selects the names of the children of the context node. The path expressions given above all select nodes in a tree. However, the / operator can also be used as a simple mapping operator to compute atomic values for each node in a sequence; this example returns a sequence of strings, each being the name of a child element of the context node. I refer to this kind of expression as a simple mapping expression , and because this chapter is all about expressions that operate on nodes, I will cover simple mapping expressions in Chapter 10.