How does the RegisterXLL() method of the Excel.Application object work for loading DLLs, and what prerequisites are needed?

The RegisterXLL() method loads a DLL into the Excel application's process, effectively executing its code. This technique requires Microsoft Office (Excel) to be installed on the system and works with any DLL that exports the required XLL interface. The article demonstrates this via rundll32, JScript, and PowerShell, with a test DLL like a simple messagebox.