storage size of "bitstring"?

Hi,

Two short questions:

1) What storage size does the "bit(n)" data type have? Is it one byte per 8
bits (plus a "length" byte)? I didn't find this in neither the docs nor the
list archives ...

2) Additionally, how much storage space does a functional index which
returns "boolean" approx. take? Will it be a bitmap?

Reason: i need to add some flags to a row, and i don't want to spend an
entire byte per flag on a "boolean" column (even worse, new flags could
probably be added in the future) - would it make sense to use
a bitstring, together with a functional index on any "interesting" bit in
that case?

thanks,

Alex