In several places (e.g. Making separator and button menu in customized Toolbar using ArcObjects?) I have seen it mentioned that the way to add a separator for add-in menus and toolbars is adding the attribute
separator="true" to the button in the config.xml file like:
<Button refID="test105_addin.button_1" separator="true"/>.
However, I can only get it to work with ArcGIS 10.3 and not with 10.1/10.2.2.
Does anybody know how a separator is added using ArcGIS 10.1 (or 10.2.2)?