Returns a JSON serializable represenation of a ``MzmlPrecursor``
        class instance. Use :func:`maspy.core.MzmlPrecursor._fromJSON()` to
        generate a new ``MzmlPrecursor`` instance from the return value.

        :returns: a JSON serializable python object

def _reprJSON(self):
        """Returns a JSON serializable represenation of a ``MzmlPrecursor``
        class instance. Use :func:`maspy.core.MzmlPrecursor._fromJSON()` to
        generate a new ``MzmlPrecursor`` instance from the return value.

        :returns: a JSON serializable python object
        """
        return {'__MzmlPrecursor__': (self.spectrumRef, self.activation,
                                      self.isolationWindow, self.selectedIonList
                                      )
                }