Continue 'Slide to note', but also do Volume slide
Where [5][x][y] means "either slide the volume up x*(ticks - 1) or slide the volume down y*(ticks - 1), at the same time as continuing the last 'Slide to note'". It is illegal for both x and y to be non-zero. You cannot slide outside the volume range 0..64. The period-length in this channel's division is a parameter to this effect, and hence is not played.
