Hi Marc, You frequently have u8vectors generated by various routines in Scheme and that for that reason of course are movable, and, then you want to take it through a function in the C world (such as, a hashing function provided by some C library), and suddenly you know that you will need to ensure that that object not will move around for a bit. The same applies to some vectors and strings. The ordinary way to do this is to generate a new empty ___STILL object and then copy over all the content. I guess this is for memory-technical reasons - ___STILL objects always have their own allocation, whereas movable objects are swamped up in the memory blocks, or? So just wanted to check with you if live switching between movable and ___STILL could be feasible. I presume it's not. Thanks!