'**Arguments:**
xvals           A list of x values (in data coordinates) at which to draw ticks.
yrange          A list of [low, high] limits for the tick. 0 is the bottom of
the view, 1 is the top. [0.8, 1] would draw ticks in the top
fifth of the view.
pen             The pen to use for drawing ticks. Default is grey. Can be specified
as any argument valid for :func:`mkPen<pyqtgraph.mkPen>`'

def __init__(self, xvals=None, yrange=None, pen=None):

    if (yrange is None):
        yrange = [0, 1]
    if (xvals is None):
        xvals = []
    UIGraphicsItem.__init__(self)
    if (pen is None):
        pen = (200, 200, 200)
    self.path = QtGui.QGraphicsPathItem()
    self.ticks = []
    self.xvals = []
    self.yrange = [0, 1]
    self.setPen(pen)
    self.setYRange(yrange)
    self.setXVals(xvals)
