The description of usage of `Builtin` and `Predefined` class in <Evaluation of an Expression> is incorrect? about mathics-development-guide

[mmatera]

@CallmeNezha, you are right: Predefineds are Builtins that represent the behaviour and rules or Symbols like True or Pi. So, Predefined objects does not have leaves. Also, there are Expressions which to not take parameters like ``MemoryInUse[]```. Those are represented by Builtins. So, the right sentence would be something like

"Functions which take no parameters are generally subclassed off of the Builtin class, while Symbols are subclassed off of the Predefined class. "

Over the weekend I will try to rewrite this section.

[rocky]

I might have gotten this wrong. Suggest how you think this should be worded.

[rocky]

@CallmeNezha In branch https://github.com/Mathics3/mathics-development-guide/tree/builtin-vs-predefined I made a pass at addressing the concerns you raise. As I work on the system, I understand more about it. So in that respect I am no different than anyone else, including yourself.

If you can, please look that over to see if this now helps and matches your expectation. @mmatera has the most experience with all of this, so we'll just wait for him to look over before I commit this to the master branch and update the readthedocs material online.