func:`func2` will be used for
        keys 'd' and 'e'.  This could also be written as::

            __conflict_solve = dict(func1='a b c',func2='d e')

        These functions will be called for each key they apply to with the
        form::

            func1(self['a'], other['a'])

        The return value is used as the final merged value.

        As a convenience, merge() provides five (the most commonly needed)
        pre-defined policies: preserve, update, add, add_flip and add_s. The
        easiest explanation is their implementation::

            preserve = lambda old,new: old
            update   = lambda old,new: new
            add      = lambda old,new: old + new
            add_flip = lambda old,new: new + old  # note change of order!
            add_s    = lambda old,new: old + ' ' + new  # only for str!

        You can use those four words (as strings) as keys instead
        of defining them as functions, and the merge method will substitute
        the appropriate functions for you.

        For more complicated conflict resolution policies, you still need to
        construct your own functions.

        Examples
        --------
        This show the default policy:

        >>> s = Struct(a=10,b=30)
        >>> s2 = Struct(a=20,c=40)
        >>> s.merge(s2)
        >>> sorted(s.items())
        [('a', 10), ('b', 30), ('c', 40)]

        Now, show how to specify a conflict dict:

        >>> s = Struct(a=10,b=30)
        >>> s2 = Struct(a=20,b=40)
        >>> conflict = {'update':'a','add':'b'}
        >>> s.merge(s2,conflict)
        >>> sorted(s.items())
        [('a', 20), ('b', 70)]
        c