QTabBar and tabbed document interfaces on OS X

The QtTabBar implementation on OS X is currently not ideally suited for creating tabbed document interfaces. It does provide a "documentMode" which is supposed to provide a style as used in Terminal.app or Safari (cf. https://git.reviewboard.kde.org/r/128880/file/3353/) but that is in reality quite different (cf. https://bugsfiles.kde.org/attachment.cgi?id=100990).

In addition, setting document mode does not lead to a behaviour that's suitable for a tabbed document interface, i.e. no (or less severe) truncation of the tab texts (ElideNone) and NO adjustment of the parent window but appearance of scroll buttons instead. Adjusting the window width may be appropriate for dialogs, but it's not for tabbed document interfaces.
Both these aspects can be set with the corresponding class methods, but they should IMHO be toggled when activating documentMode.

However, I would like to let you take into consideration that OS X applications that use this particular style of tabbed documents typically do not have toolbars between the tabbar and the window's titlebar. One can argue to what extent the interface displays tabbed documents at all; having the tabs "attached to" a toolbar above it instead of to the documents below it detaches it just too much and makes it look wrong IMHO.
I also think that QStyle::PM_TabBarBaseOverlap should not return the same value in documentMode as it does in standard mode.

In my opinion, the easiest way to get a usable tabbed document interface that doesn't look out of place nor odd is to use the Fusion style for QTabBar if that widget is to be used in such an interface:

https://git.reviewboard.kde.org/r/128880/file/3355/

Full discussion and other screenshots at
https://bugs.kde.org/show_bug.cgi?id=363473
and
https://git.reviewboard.kde.org/r/128880/