The boxerrorbars style is only relevant to 2-d data plotting. It is a
combination of the boxes and yerrorbars styles. The boxwidth will come
from the fourth column if the y errors are in the form of ``ydelta'' and the
boxwidth was not previously set equal to -2.0 (set boxwidth -2.0) or from
the fifth column if the y errors are in the form of ``ylow yhigh''. The
special case boxwidth = -2.0 is for four-column data with y errors in the
form ``ylow yhigh''. In this case the boxwidth will be calculated so that each
box touches the adjacent boxes. The width will also be calculated in cases
where three-column data are used.
The box height is determined from the y error in the same way as it is for
the yerrorbars style—either from y-ydelta to y+ydelta or from ylow to
yhigh, depending on how many data columns are provided.