How to close current and select left tab?

I uploaded another version of the event-based prototype we did back in january, maybe you like to give it another try. While using it over the last couple of month I came across weird situations when closing tabs, that were not active or not connected to the source file-display. These topcis have been addressed and since then, I found it to work stable.
ActivateLeftTabOnClose: Event: ActivateLeftTabOnClose (switch to left instead of previously used tab)