  We study extensions of sets and functions in general metric measure spaces.
We show that an open set has the strong BV extension property if and only if it
has the strong extension property for sets of finite perimeter. We also prove
several implications between the strong BV extension property and extendability
of two different non-equivalent versions of Sobolev $W^{1,1}$-spaces and show
via examples that the remaining implications fail.
