Microsoft released Windows PowerShell 3.0 Language specification to the public. This is a 334 pages of documentation and has tons of information on how the language is implemented. This specification is made available as part of the Microsoft Open Specifications program.
This specification defines the PowerShell language, the built-in cmdlets, and the use of objects via the pipeline. You can download the PowerShell 3.0 Language Specification @ http://www.microsoft.com/en-us/download/details.aspx?id=36389