Visualisations of the B4 and T4 fields. Panels a) and b): overlapping tubular domains in the dipolar and sigmoidal dipole backgrounds respectively. Panels c) and d): magnetic field lines of the corresponding field. In B4 c) the sequentially applied twists have opposing chirality and field lines are braided, whilst in T4 d) the twists have the same chirality and field lines are twisted (non-uniformly).