Today I like to point you to the official Microsoft PowerShell Language Definition. As a seasoned PowerShell scripter, you can gain a lot of inside knowledge by looking at the formal definition of the PowerShell language itself.
The language definition explains a zillion of practically relevant details such as a comprehensive list of predefined variables, built-in keywords, operator precedence, and so much more. You can find the language definition online here:
The 13 chapters have also been translated to a number of languages. The German edition can be found here: