If you don't know what UB or IDB is, you probably don't want to write a book pertaining to C, :)
Could be intel debugger, could be undefined behavior, could be implementation defined behavior. I tested them on a group of about 15 C devs, mixture of embedded, linux, DSP, and other volken.
Got the same guesses I made and a lot of question marks.
It's easy to run your mouth but not actually contribute, you might consider your role in this process before commenting again.