What is the difference between the RunScript("bob") and the selenium.browserbot.getCurrentWindow().bob()

Question

Just wondering what the difference between using the runscript and browserbot.getCurrentWindow() method of calling javascript methods.

Is the runScript approach simply a way to inject extra JS to the page and the getCurrentWindow() a way to invoke existing code?

One curious thing I noticed is that

selenium.browserbot.getCurrentWindow().pickFeature(new OpenLayers.Feature.Vector(new OpenLayers.Geometry.Point(477504.5,162568.5)))

Will complain about OpenLayers (external JS library we use).