Add-in type: Content, Task pane, Mail
<AppDomains> <AppDomain>AppDomain1</AppDomain> <AppDomain>AppDomain2</AppDomain> </AppDomains>
By default, your add-in can load any page that is in the same domain as the location specified in the SourceLocation element. To load pages that are not in the same domain as the add-in, specify the domains by using the AppDomains and AppDomain elements. This element can't be empty.
For more information, see Office Add-ins XML manifest.