The axis portion of an XPath location step specifies, like the axis of a two-dimensional graph, the direction in which to locate something relative to some starting point. There is an axis corresponding to each of the basic XPath tree model relationships:
parent::
child::
ancestor::
descendant::
ancestor-or-self::
descendant-or-self::
preceding::
following::
preceding-sibling::
following-sibling::
self::
attribute::
namespace::
Use XPath Axes to Navigate through XML Data