Differential SSTL_18 voltage levels

I am confused about the input voltage levels for differential SSTL_18.

cyc3_ciii52001.pdf page 1-13 has a table that shows the levels for Vswing(DC), Vx(AC), Vswing(AC), and Vox(AC). I do not know what they mean. Can someone explain or post a drawing of the waveforms showing the acceptable voltage levels?

Thanks

Bob