These functions are officially part of Lua's standard libraries. However, except in their own subsections, they are not mentioned in the reference manual, and their own subsections have no useful keyword like "vararg" and "multiple results". The free version of the Lua book is obsolete in this respect.
When you know how and when these functions are used, then the manual makes perfect sense. But if you do not, then you cannot even find them there (except by reading it through). I would say that some examples and cross-references would be very helpful.
Cheers,
V.
