but it does use up a bit of toolbar space.
Absolutely right. That's why I thought of an implementation as a command button, as some users might not want to have that feature. But at least you can set up that command button when you like to.
Actually I'm a bit influenced by the highly customizable toolbars in former Microsoft applications (before they ruined that feature by introducing the "ribbons"
). In Outlook, for instance, I've set up quite the same like illustrated above - and it became an absolutely essential thing for me to toggle different views this way. That's what set the impulse for my request foremost.
If the end result is the same, maybe they should display the same little subscript numbers Ctrl-clicking a column header displays.
That would be a solution as well, though it wouldn't offer the toggling of the sorting sets. And it could be more clearly for the user to see the sorting set written in words (like "Year/ Artist/ Album") instead of the subscript numbers. It could also be problematic when a column which is used for sorting is hidden/not displayed, isn't it?
EDIT:
@Zak: I forgot: your hidden feature in the other thread over there, with CTRL-clicking column-headers for combined sorting, is great
. Never ever I would have noticed that.