def delete element
      if element.kind_of? Element
        @element.delete element
      else
        el = self[element]
        el.remove if el
      end
    end
def delete element
      if element.kind_of? Element
        @element.delete element
      else
        el = self[element]
        el.remove if el
      end
    end
Deletes a child Element
 element::
   Either an Element, which is removed directly; an
   xpath, where the first matching child is removed; or an Integer,
   where the n'th Element is removed.
 Returns:: the removed child
  doc = Document.new '<a><b/><c/><c id="1"/></a>'
  b = doc.root.elements[1]
  doc.root.elements.delete b           #-> <a><c/><c id="1"/></a>
  doc.elements.delete("a/c[@id='1']")  #-> <a><c/></a>
  doc.root.elements.delete 1           #-> <a/>