The xerrorlines style is only relevant to 2D data plots.
xerrorlines is like linespoints, except that a horizontal error line is
also drawn. At each point (x,y), a line is drawn from (xlow,y) to (xhigh,y)
or from (x-xdelta,y) to (x+xdelta,y), depending on how many data columns are
provided. The appearance of the tic mark at the ends of the bar is controlled
by set errorbars. The basic style requires either 3 or 4 columns:
3 columns: x y xdelta
4 columns: x y xlow xhigh
An additional input column (4th or 5th) may be used to provide variable color.
