Returns a collection of elements that are present in the DOM before each element in the original collection.
var svg = Pablo(demoElement).svg({height: 60});
svg.append(Pablo.circle({r: 30, cx: 30, cy: 30}))
.append(Pablo.circle({r: 30, cx: 100, cy: 30}))
.append(Pablo.circle({r: 30, cx: 170, cy: 30, fill:'green'}))
.append(Pablo.circle({r: 30, cx: 240, cy: 30}));
svg.children('circle[fill=green]')
.prevSiblings()
.attr({'fill': 'purple'})