unions or automatic aggregates cannot be initialized. Why?

[A. Krishna Murthy]

	Hi folks,

	In the definitive text 'The C Programming Language' by
	Brian W kernighan and Dennis M Ritchie,
	Appendix A: C Reference Manual, section 8.6 Initialization,
	paragraph four, emphatically states

	"It is not permitted to inititalize unions or automatic aggregates."

	Why?

	Note:
	The above statement is with regard to the definition of the language
	and NOT to any implementation difficulties.

	Answers will be very much appreciated.

	kris.