RTFM
The pages within the links to the left contain an in depth description of everything contained within both the IsForth kernel and the extensions thereto. This is a work in progress and you will see the content here grow and change over time.
The documentation has been split into two parts. The first part (under the Info heading to the left) contains various interesting (or not) information about these sources, Forth in general and IsForth itself.
Then we have the documentation for every source file used to create the IsForth kernel and the extensions to the kernel. I have tried to not make the assumption that the reader will be a Forth expert but I have also tried not to treat the reader as if he / she needs everything explained in minute detail.
If something is not clear from my description then let me know and I will try to help you understand it. If a better description can be found I can change things here to make it easier for you the readers.