docs: def locateChild(self, ctx, segments):
          """
          Attempt to locate the child via the '.fragment' attribute, then fall
          back to normal locateChild behavior.
          """
          if self.fragment is not None:
              # There are still a bunch of bogus subclasses of this class, which
              # are used in a variety of distasteful ways.  'fragment' *should*
              # always be set to something that isn't None, but there's no way to
              # make sure that it will be for the moment.  Every effort should be
              # made to reduce public use of subclasses of this class (instead
              # preferring to wrap content objects with
              # IWebViewer.wrapModel()), so that the above check can be
              # removed. -glyph
              lc = getattr(self.fragment, 'locateChild', None)
              if lc is not None:
                  x = lc(ctx, segments)
                  if x is not NotFound:
                      return x
          return super(MantissaViewHelper, self).locateChild(ctx, segments)