As far as I'm aware, global
has the same meaning in documentation comments as in normal code. It's just a namespace alias which allows you to avoid conflicts between namespace names and type names. See MSDN on the Global Namespace Alias for more details.
Note that this isn't the same as extern aliases which are used when you have two types with the same fully-qualified names, in different assemblies. Your question talking about "different roots" suggests you might be getting confused with extern aliases, but it's hard to know for sure.