docs: def _sync_from_disk(self):
          """Read any changes made on disk to this Refpkg.
  
          This is necessary if other programs are making changes to the
          Refpkg on disk and your program must be synchronized to them.
          """
  
          try:
              fobj = self.open_manifest('r')
          except IOError as e:
              if e.errno == errno.ENOENT:
                  raise ValueError(
                      "couldn't find manifest file in %s" % (self.path,))
              elif e.errno == errno.ENOTDIR:
                  raise ValueError("%s is not a directory" % (self.path,))
              else:
                  raise
          with fobj:
              self.contents = json.load(fobj)
  
          self._set_defaults()
          self._check_refpkg()