FWIW my intuition is that any functions, classes, constants, whatever - things that I could write myself if I had to - are “standard library”. “Core language” r

FWIW my intuition is that any functions, classes, constants, whatever - things that I could write myself if I had to - are “standard library”. “Core language” refers to syntactic or semantic features of the language that would require modifying the compiler or interpreter to introduce.