  We introduce an operational entanglement classification of symmetric mixed
states for an arbitrary number of qubits based on stochastic local operations
assisted with classical communication (SLOCC operations). We define families of
SLOCC entanglement classes successively embedded into each other, we prove that
they are of non-zero measure, and we construct witness operators to distinguish
them. Moreover, we discuss how arbitrary symmetric mixed states can be realized
in the lab via a one-to-one correspondence between well-defined sets of
controllable parameters and the corresponding entanglement families.
