The META4_CHARACTER is just like the other meta keys except that it is now sticky. That is, Meta4-C-D-E-F-G invokes the meta4 versions of C, D, E, F and G. This effect lasts until meta4 is invoked again. Additionally, the Meta4 characters ^h, SPACE, h, i, j, k, x, H, I, J, K, L and X have been bound in such a way that BIND ^[ META4_CHARACTER now gives a vi editing mode.
It will stay 'stuck' until it is unstuck with any key bindings that happen to activate the META4_CHARACTER.