All builtins now return an exit status of 2 for incorrect usage. Bash now defaults to using command-oriented history. The PS1, PS2, PATH, and IFS variables may now be unset. The restricted shell mode has been expanded and is now documented. Integer constants have been extended to base 64.
More file types are available for the visible-stats mode.
Changes of interest in the Bash implementation a. There is a new autoconf-based configuration mechanism. More things have been moved from Posix mode to standard shell behavior. The YACC grammar is smaller and tighter, and all 66 shift-reduce conflicts are gone. Several parsing bugs have been fixed.