[R] Why are there typeof(), mode() and storage.mode()?

[Peng Yu]

According to R-lang.pdf (Section 2):

Function mode gives information about the mode of an object in the
sense of Becker,
Chambers & Wilks (1988), and is more compatible with other
implementations of the S
language. Finally, the function storage.mode returns the storage mode
of its argument
in the sense of Becker et al. (1988).

Could somebody give an explanation, without the reference to S (as the
user may not know R enough, let along S), on why there are the three
functions typeof(), mode() and storage.mode(), how and when to use
them, what are the implication of these functions? The above
explanation on mode and storage.mode says nothing except pointing the
reader to two other old papers. Could somebody improve the document so
that users without S background can still understand them?