V4 DSC language extensions

DSC adds three new functions as language extensions to support declaring the expected state of a machine:

• Configuration: The configuration keyword is a DSC function that declares a set of operations to perform on a target system.
• Node: The node configuration keyword is a DSC function that declares the target host to perform operations on.
• Import-DscResource: This looks like a PowerShell cmdlet but really is a keyword. It locates the DSC resources needed to parse and compile the DSC configuration script.