Xfce 4.12 still hasn't been released yet and it's running months behind schedule. Xfce 4.12 will be a major update to the lightweight desktop that's becoming an increasingly used alternative to Unity and the GNOME Shell. Here's an update on some of the completed features.
Early in the Xfce 4.12 development cycle there was talk of being ported to GTK3, but in the end, it will still be GTK2-based. GTK+2 is the default for Xfce 4.12 but there will be partial support for GTK+3 with Xf* programs being optionally allowed to support GTK3 in parallel (libxfce4ui already supports an optional parallel GTK3 install).
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