Extra preferences are displayed on the Extra tab of the Preferences dialogs on the Articles, Pages and Editions main tab.
The extra preferences of the Articles main tab are defined in TedSystemAddInExpress, under Dialogs folder, in the ExtPreferences.vb file.
The extra preferences of the Pages and Editions main tab are defined in TedSystemAddInExpress, under Dialogs folder, in the ExtPreferences.vb file - it contains two Extra tabs, whereas the first one is for the Pages main tab, and the second one is for the Editions main tab.
Note for the Perforce users
Check-out ExtPreferences.Designer.vb, ExtPreferences.resx, and ExtPreferences.vb.