Say you have a collection of radio buttons. They’re NSButton instances, and NSButton inherits from NSControl. Radio buttons’s mutual exclusivity is implemented by … With the correct setup, you can set 1 out of 100 radio buttons to .on and have the previous selection turned off for you automatically. That’s neat.
I still use TextMate for some things: editing documents quickly, scripting in Ruby, navigating project folders of foreign code bases (especially when they’re not using my main language so I could use Xcode, e.g. Java projects), and finding and replacing text. But it always bugged me that when I move around code and indent and outdent and whatnot, that sometime lines with nothing but whitespaces would be saved. Or I’d combine stuff and have 10 trailing spaced all of a sudden. I do show invisible characters, but I don’t want to pay attention to that kind of stuff when I’m coding.