code: function drawHoverHighlightBars(dataArray) {
  		var hoverBar = parent.svgHoverRoot.selectAll('rect.highlightbar').data(dataArray);
  		hoverBar.attr('x', valueX)
  				.attr('width', xBar.rangeBand());
  		hoverBar.enter().append('rect')
  				.attr('x', valueX)
  				.attr('y', 0)
  				.attr('height', parent.height)
  				.attr('width', xBar.rangeBand())
  				.classed('highlightbar clickable', true);
  		hoverBar.exit().remove();
  	}
docs: Render a "highlight bar" over a set of bars.
  
  @param {array} dataArray An array of data elements for which to render highlight bars over.
  Pass an empty array to remove all bars.