code: def set(self, name, value):
          
          attr = self.getAttribute(name)
          if attr is None:
              attr = Attribute(name, value)
              self.append(attr)
          else:
              attr.setValue(value)
docs: Set an attribute's value.
          @param name: The name of the attribute.
          @type name: basestring
          @param value: The attribute value.
          @type value: basestring
          @see: __setitem__()