Well I went looking around for an XSD schema that could validate XML comments I place in code for documentation. Either Microsoft never delivered one, or I completely failed to find it. Amazing that I found many people looking for it, but nobody willing to write it. So I did, you can get it here:
The schema will validate all of xml comments in the .NET BCL 2.0 through 4.0 so it should be close enough for whatever you have in mind. Some of the Microsoft specific stuff (PermissionSet) I kinda punted on as I couldn’t find anything consistent about what they were producing. Other than that though it should be complete enough.