Uses the same method than http://wrobstory.github.io/2013/11/D3-brush-and-tooltip.html with slight adjustements.
The brush overlay is added before (ie. under) the features on the plot.
Mouse events on the dots are transmitted to the brush area, thus allowing tooltips to show up and allowing the user to start a selection on a dot.
An opposite method could be to add the brush after (ie. on the top of) the features on the chart, then transmitting mouse events from the brush area to these features: "Cooperative" brush and tooltip II