In the programming forum, there have been multiple posts best answered by pointing the OP at the AVR libc docs. I usually reply something like:
According to the Arduino homepage
The Arduino language is based on C/C++. It links against AVR Libc and allows the use of any of its functions; see its user manual for details.
The user manual for AVR libc is here:
avr-libc: AVR Libc
And the page on string functions is here:
avr-libc: <string.h>: Strings
The info is there, but new programmers aren’t going to know what libc is or what it’s for.
I think that somewhere fairly prominent on the homepage we need a sentence to the effect:
The arduino programming environment includes libc, which contains useful functions not specific to the arduino such as math functions, string and character manipulation, and time/date functions.
That is, not just a link to libc but also a note on why you need to know what’s in it.