code: def setPrefix(self, p, u=None):
          
          self.prefix = p
          if p is not None and u is not None:
              self.addPrefix(p, u)
          return self
docs: Set the element namespace prefix.
          @param p: A new prefix for the element.
          @type p: basestring
          @param u: A namespace URI to be mapped to the prefix.
          @type u: basestring
          @return: self
          @rtype: L{Element}