def add element=nil
      rv = nil
      if element.nil?
        Element.new("", self, @element.context)
      elsif not element.kind_of?(Element)
        Element.new(element, self, @element.context)
      else
        @element << element
        element.context = @element.context
        element
      end
    end
def add element=nil
      rv = nil
      if element.nil?
        Element.new("", self, @element.context)
      elsif not element.kind_of?(Element)
        Element.new(element, self, @element.context)
      else
        @element << element
        element.context = @element.context
        element
      end
    end
Adds an element
 element::
   if supplied, is either an Element, String, or
   Source (see Element.initialize).  If not supplied or nil, a
   new, default Element will be constructed
 Returns:: the added Element
  a = Element.new('a')
  a.elements.add(Element.new('b'))  #-> <a><b/></a>
  a.elements.add('c')               #-> <a><b/><c/></a>