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http://msdn.microsoft.com/en-us/library/b2s063f7.aspx-- XML Documentation Comments (C# Programming Guide)
start with http://blogs.msdn.com/sandcastle/ to understand Sandcastle and it's architecture. Also please see the following:
- Steps for generating CHM/HxS builds - http://blogs.msdn.com/sandcastle/archive/tags/Running+Builds/default.aspx
- Sandcastle web site - http://www.sandcastledocs.com
Sandcastle - Documentation Compiler for Managed Class: http://sandcastle.codeplex.com/
Sandcastle Help File Builder: http://shfb.codeplex.com/