Sets whether @tool_item is visible when the toolbar is docked
vertically. Some tool items, such as text entries, are too wide to be
useful on a vertically docked toolbar. If @visible_vertical is %FALSE
@tool_item will not appear on toolbars that are docked vertically.
Sets whether @tool_item is visible when the toolbar is docked vertically. Some tool items, such as text entries, are too wide to be useful on a vertically docked toolbar. If @visible_vertical is %FALSE @tool_item will not appear on toolbars that are docked vertically.