Unmanaged Reflection API
Most metadata can be accessed using managed reflection. In a few cases, metadata is difficult to retrieve using the classes provided in managed reflection. There are also cases where managed reflection does not provide the best possible performance.
Using the unmanaged reflection API requires familiarity with the Common Language Infrastructure (CLI) documentation, especially "Partition III: CIL Instruction Set" and "Partition II: Metadata Definition and Semantics". The documentation is available online; see ECMA C# and Common Language Infrastructure Standards on MSDN and Standard ECMA-335 - Common Language Infrastructure (CLI) on the Ecma International Web site.