Among the many shells existing at the time of evaluation, the two most compliant were Bash and Pdksh.
At the time of evaluation, Bash was found mostly compliant with the POSIX-1003.2 standard, and its maintainer demonstrated interest in bringing the shell to full compliance. Bash already enjoys wide use among shell users, and is even included in many distributions as the default shell. Further, the abundance of documentation found both on the Internet and in the bookstore makes Bash an easy shell to use.
Of course, shell scripts must avoid using bash extensions if they want to run on any LSB system.
The two exceptions to POSIX (concerning . and non-readable files, and argv[0]) in this section are to accommodate bash. The need for exceptions should be reviewed if bash changes or POSIX changes to remove the conflict. Future versions of this standard may also consider exceptions for pdksh or other almost-compliant shells, if they seem to be warranted.