https://www.mathworks.com/help/stateflow/api/stateflow.atomicbox.html
Stateflow.AtomicBox - Atomic box in chart, state, box, or function - MATLAB
Use Stateflow.AtomicBox objects to encapsulate graphical, truth table, MATLAB, and Simulink functions in a separate namespace.
atomic boxstateflowchartfunctionmatlab