from Section 4.4: Chapter 8 revisits the definition and declaration criteria to a depth that will cause decompression sickness when you surface.

8.1. Government Health Warning
The previous chapters have introduced the fundamentals of the language and have covered nearly all of the language that the Standard defines. There are a number of murky and convoluted backwaters left unexplored on grounds of sympathy and compassion for the sufferer, and some without any better home. This chapter gathers them together—it's the toxic waste dump for the nasty bits of C.
-- Mike Banahan, Declan Brady and Mark Doran,The C Book, Second Edition, Addison Wesley, 1991