4 columns: x y xdelta ydelta
6 columns: x y xlow xhigh ylow yhigh
If data are provided in an unsupported mixed form, the using filter on the plot command should be used to set up the appropriate form. For example, if the data are of the form (x,y,xdelta,ylow,yhigh), then you can use
plot 'data' using 1:2:($1-$3):($1+$3):4:5 with xyerrorbars
An additional input column (5th or 7th) may be used to provide variable (per-datapoint) color information.