Are default Nodes open too?

As we all know dynamo is open-source but does that mean its free to use or you are able to access and use the codes behind?

I have been trying to look through the default nodes for their background codes so i could use them in creating my RPS scripts ,I knew that they may be in C# but at least I could understand the API code used.

If its available can someone share it…!

Said information should be on the github, but they do make calls to non-open source code within other libraries like Autodesk Solid Modeler.