This can be used by applications to indicate that a paned is expected to be actively used by the users for configuring the UI, and needs a prominent handle.
https://bugzilla.gnome.org/show_bug.cgi?id=738860
cf0c9eb GtkPaned: Add a "wide-handle" property
docs/reference/gtk/gtk3-sections.txt | 3 ++
gtk/gtkpaned.c | 82 +++++++++++++++++++++++++++++++++-
gtk/gtkpaned.h | 6 +++
gtk/gtkstylecontext.h | 10 +++++
4 files changed, 100 insertions(+), 1 deletion(-)
Upstream: git.gnome.org