I think that was actually a bug in the debugger, or inspector, not in MonticelloRepositoryBrowser.
And yes, this appear to be dead code. I found it before finding the actual browser, and thought it might be a good place to start exploring Monticello.
I tried the old debugger in my new latest image (in the hope that syntax highlighting would not be broken there), but I realised it advertised no keyboard shortcut for stepping through the code���
Starting to wonder if I should go back to spending my evenings playing Elite Dangerous, and come back in a few weeks when stuff is hopefully less buggy everywhere :-(