code: def set(self, name, value):
          
          self.provider(name).__set(name, value)
          return self
docs: Set the I{value} of a property by I{name}.
          The value is validated against the definition and set
          to the default when I{value} is None.
          @param name: The property name.
          @type name: str
          @param value: The new property value.
          @type value: any
          @return: self
          @rtype: L{Properties}