For whatever reason, I’m reduced to remotely debugging some code with the random version of xemacs that happens to be installed on the remote Mac system. (I’d rather use my favourite editor, the wonderful gedit, but that’s not really practical in this particular instance.)
Anyway, it turns out that I can’t live happily without syntax highlighting, which isn’t turned on by default. To turn it on, all you need to do is type
M-x font-lock-mode (I have no idea why it’s called font-lock rather than “syntax highlighting”).