gtk:toolbar-set-drop-highlight-item (toolbar item index)

toolbar -- a gtk:toolbar widget
item -- a gtk:tool-item widget, or nil to turn of highlighting
index -- an integer with a position on toolbar

Highlights the toolbar to give an idea of what it would look like if item was added to the toolbar at the position indicated by index. If the item argument is nil, highlighting is turned off. In that case index is ignored.

The tool item passed to this function must not be part of any widget hierarchy. When an item is set as drop highlight item it can not added to any widget hierarchy or used as highlight item for another toolbar.