Panel a: schematic drawing of a twisted loop. Green arrows show the longitudinal and azimuthal magnetic field in selected locations. Orange dot-dashed line denotes the “skeleton line”, i.e. the magnetic field line connecting centres of loop footpoints. Panel b: schematic drawings of the cross-loop polarisation gradient (CLPG) patterns in cases when a loop is observed from its top and from its side. Blue forward slash hatching and red backslash hatching correspond to positive and negative values of Stokes V, respectively. Black dashed lines denote Stokes V = 0.