When you create a project in vsprvsext, this attribute is automatically applied with an empty string value. You can set its value in vsprvslong by selecting the Properties for the project from the File menu, and then by clicking Assembly Information. The attribute is saved in the AssemblyInfo file in your project, and it must be removed before you can specify it in code; otherwise, you will get an error that the attribute cannot be applied multiple times.

When you right-click the assembly file in File Explorer, this attribute appears as the Comments value on the Version tab of the file properties dialog box.