Scrolling randomly through the document my eyes almost popped when I saw [Level 3, Chapter 16: Performance]:

  A pointer to a collection of objects of unknown number. These functions
  should use the VLA notation:
 
      void func(size_t n, double a[n]);

I had no idea this was possible. Do compilers actually do anything with this information or is it just informative?

EDIT: I didn't get a warning out of gcc

  #include <stddef.h>
 
  int last(size_t n, int a[n]) {
    return a[n-1];
  }
 
  int main() {
    int a[] = {0, 1, 2, 3, 4};
    size_t siz = sizeof(a) / sizeof(a[0]);
    return last(siz+1, a);
  }

Compile:

  $ cc --version
  cc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
  Copyright (C) 2013 Free Software Foundation, Inc.
  This is free software; see the source for copying conditions.  There is NO
  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

  $ cc -Wall -Wextra -std=c11 staticarr.c -o staticarr && ./staticarr ; echo $?
  254

clang 3.8 warns about differing things:

  $ clang-3.8 -Weverything -std=c11 staticarr.c -o staticarr && ./staticarr ; echo $?
  staticarr.c:3:25: warning: variable length array used [-Wvla]
  int last(size_t n, int a[n]) {
                          ^
  staticarr.c:3:5: warning: no previous prototype for function 'last' [-Wmissing-prototypes]
  int last(size_t n, int a[n]) {
      ^
  2 warnings generated.

Still, it's a neat idea from a documentation point of view, and GNU-like compilers seem to accept it.

A bit before is more explanation of on the arr[static ?] notation. I was aware of this and usually prefer to use (Clang/GCC) function annotations to indicate NULL-ness of pointers and such, but I see the advantage in some situations. I don't agree with everything in the document, but it contains a lot of cool things.