Begin with a / to select the root node
Independent of the context node
/child::PERIODIC_TABLE/child::ATOM is an XPath expression that selects all ATOM elements.
/child::PERIODIC_TABLE/child::ATOM[1] is an XPath expression that selects the first ATOM element.
/child::PERIODIC_TABLE/child::ATOM/child::SYMBOL is an XPath expression that selects all SYMBOL elements.
/child::PERIODIC_TABLE/child::ATOM[ATOMIC_NUMBER="3"] is an XPath expression that selects Lithium.
/descendant::ATOM[SYMBOL="He"]/child::DENSITY/attribute::UNITS is an XPath expression that selects the units in which the density of Helium is given.
/child::PERIODIC_TABLE/child::ATOM/child::* is an XPath expression that selects all the child elements of ATOM elements.
/descendant::* is an XPath expression that selects all the elements in the document.
/descendant-or-self::node() is an XPath expression that selects all non-attribute, non-namespace nodes in the
document.