When iTunes 10 was released back on the 1st of September, there was a lot of talk about the iTunes team’s decision to move the “stoplight buttons” to the left side of the toolbar instead of the default place on the very top.
iOS and Mac developers know that both platforms are guided by strict Human Interface Guides (HIGs) that help maintain consistency among the myriad of third-party applications that exist. Many people made the point (myself included) that the iTunes team must think that they’re above maintaining OS consistency, making such a drastic change to the user interface.
Tonight, over a month after the release, I had the realization that maintaining application consistency slightly trumps OS consistency. I made the comment on day one that the iTunes mini player already had the vertical stoplight buttons, but I don’t even think I realized the full meaning of my comment.
Applications are often said to be inconsistent with their host system if they look differently from other applications on that system. However, look alone doesn’t really matter. As long as users are capable of easily identifying the different UI elements, applications don’t have to look like their host system. […] A different look doesn’t harm usability, as long as the individual widgets are easily recognizable, and as long as they behave the way the user expects them to.
As long as widgets are easily recognizable and behave the way the user expects them to, look doesn’t really matter. One interesting side note in regards to the stoplight buttons on iTunes is the “+” button doesn’t function the same as the rest of the OS. Regardless of the slight difference in functionality, the point remains, the widget doesn’t necessarily have to look the same to be consistent.
The next part of Mathis' article that sticks out to me speaks of internal consistency (again, emphasis added):
[…] there is a second kind of consistency: Consistency within the application itself. This is especially important if you decide to forego consistency with the host system for certain aspects of your application. Think about the rules and conventions that should apply, then apply them everywhere.
The iTunes team made a decision early on in the development of the mini-player to move the stoplight buttons to the vertical format to make the player that much smaller vertically. According to Mathis, after you depart from OS consistency, consistency within the application is even more important. For this reason, I think the move to a vertical format for the stoplight buttons was a good move, if only to maintain consistency within the application.
I think iTunes 10 is a great step forward for the application. I myself have a greater appreciation for the thought processes that the iTunes user interface team could have gone through in coming to the conclusion that the stoplight needed to be placed in a vertical arrangement.