The [numpy.ndarray documentation](https://docs.scipy.org/doc/numpy/reference/arrays.ndarray.html) states that:

> 
> An ndarray is a (usually fixed-size) multidimensional container of items of the same type and size.
> 
> 
> 

I'm surprised by the adjective *usually* here. I thought an ndarray is always of a fixed size. When is the size of an ndarray not fixed?