[Help-bash] Proposed usage of $-

[Mart Frauenlob]

Hello,

I was wondering what the proposed usage of `$-' is?
I thought it will show me all current set flags, but it is excluding 
some like posix.
The reason for this question is, that I wanted to detect if a script is 
ran in posix mode. Detect that and print a warning.
But there doesn't seem to be a representation of -o posix|--posix in $-.

$ /opt/bash42/bin/bash +o posix -c 'echo $-'
hBc
$ /opt/bash42/bin/bash --posix -c 'echo $-'
hBc

Thanks for your help

Mart