Example of the magnetic topology of a separatrix dome formed from two separatrix surfaces and an open separatrix curtain which threads through the dome. a) 3D image of the topology consisting of two negative nulls (blue dots), their spine lines (thick purple lines) and separatrix-surface field lines which arch down to the photosphere forming a dome (thin blue lines). A positive null (red dot), its spine lines (thick orange lines) and separatrix-surface field lines which form the open separatrix curtain (thin pink lines). The HCS null line (thick green line) and HCS curtain field lines (thin green lines) are also shown. b) Magnetic field two grid points above the photosphere (grey-scale contour plot) and the intersection of the skeleton features with this surface, including the separatrix dome (blue line), spines (purple crosses) and HCS curtains (green lines).