I agree that being able to read source and modify the code for experimentation are important. In my experience, the best way to read source code and experiment

I agree that being able to read source and modify the code for experimentation are important. In my experience, the best way to read source code and experiment are to get the source from the upstream repo (eg. GitHub) and read/build from that. I do this with code written in C or C++ all the time. The code is always out there (unless you're talking about proprietary software, which none of your examples above are).