def next_element
      element = next_sibling
      element = element.next_sibling until element.nil? or element.kind_of? Element 
      return element
    end
def next_element
      element = next_sibling
      element = element.next_sibling until element.nil? or element.kind_of? Element 
      return element
    end
Returns the next sibling that is an element, or nil if there is
 no Element sibling after this one
  doc = Document.new '<a><b/>text<c/></a>'
  doc.root.elements['b'].next_element          #-> <c/>
  doc.root.elements['c'].next_element          #-> nil