XPath defines twelve axes along which an XPointer may search for nodes, all from the same XPath syntax used for XSLT. These depend on context to determine exactly what they point to. For instance, consider this location path:
id("p6")/child::NAME
It begins with the id() function that returns a
node set containing the element with the ID type attribute whose
value is p6. This provides a context node for the
following location step along the relative child
axis. Other axes include ancestor,
descendant, self,
ancestor-or-self, descendant-or-self,
attribute, and more. Each serves to select a
particular subset of the elements in the document. For instance,
the following axis selects from nodes that come
after the context node. The preceding axis selects
from nodes that come before the context node.