public static int getRelativeY(final NativeEvent e, final Element target) {
        return e.getClientY() - target.getAbsoluteTop() + target.getScrollTop()
                + target.getOwnerDocument().getScrollTop();
    }
Gets the mouse y-position relative to a given element.

@param target the element whose coordinate system is to be used
@return the relative y-position
stroom-core-client-widget/src/main/java/stroom/data/grid/client/MouseHelper.java