class REXML::XPathParser

def preceding(node)

except for ancestors
preceding:: includes every element in the document that precedes this node,
in reverse document order
Builds a nodeset of all of the preceding nodes of the supplied node, 
def preceding(node)
  ancestors = []
  parent = node.parent
  while parent
    ancestors << parent
    parent = parent.parent
  end
  precedings = []
  preceding_node = preceding_node_of(node)
  while preceding_node
    if ancestors.include?(preceding_node)
      ancestors.delete(preceding_node)
    else
      precedings << XPathNode.new(preceding_node,
                                  position: precedings.size + 1)
    end
    preceding_node = preceding_node_of(preceding_node)
  end
  precedings
end