Specify an XPath expression in the corresponding text field.
This expression is evaluated in the context of the explicitly selected node, if any, and in the context of the implicitly selected element otherwise.
The evaluation of the XPath expression must return a nodeset. If this nodeset exclusively contains contiguous siblings, all the nodes in the nodeset are selected. Otherwise, first node (in document order) of the nodeset is selected.
If the evaluation of the expression returns attributes, the corresponding elements are selected.
It is not possible to select the document node or sibling nodes of the root element.