.. currentmodule:: bitstring

The pos will also used as a default for the :meth:`BitArray.overwrite` and :meth:`BitArray.insert` methods.

The bit position is modified by methods that read bits, as described in :attr:`~ConstBitStream.pos`, but for the mutable BitStream it is also modified by other methods:

• If a methods extends the bitstring (+=, append) the pos will move to the end of the bitstring.
• If a method otherwise changes the length of the bitstring (prepend, insert, sometimes replace) the pos becomes invalid and will be reset to 0.