Reference for HLSL

The HLSL reference documentation specifies the language characteristics. It is broken into several sections.

Language Syntax (DirectX HLSL) - Programming shaders in HLSL requires that you understand the language syntax, that is, how you write HLSL code. This includes code to declare and initialize variables, write user-defined shader functions, and add flow control statements to make your functions more powerful.
Shader Models vs Shader Profiles - The HLSL compiler implements rules and restrictions based on shader models. The code in each vertex shader, geometry shader (if you are using Direct3D 10) and pixel shader are validated against a shader model, which you supply at compile time.
Intrinsic Functions (DirectX HLSL) - HLSL has many intrinsic functions. These are implemented and tested so that you can use them knowing that they are already debugged and they perform well. If you choose to write your own functions, see the language syntax section for writing user-defined functions.
Appendix (DirectX HLSL) - The appendix is included for completeness. It includes a listing of the keywords and reserved words; these words cannot be used as identifiers in your programs. It also includes a listing of the language grammar for reference.