11158 on 15 February 2011 with a maximum at 01:44 UT. On top of the background context images for SDO/HMI intensity (left) and line-of-sight magnetogram (right) the location of the flare kernels is overplotted. The colours represent the time stamp from violet (the beginning) to red (the end) colours. []{data-label="fig:examples_nonflat"}](fig-nonflat.pdf){width="\textwidth"}

![Example of the flare belonging to C1 class. This M5.3-class flare ignited in NOAA 11283 on 9 June 2011 with a maximum at 01:35 UT. On top of the background context images for SDO/HMI intensity (left) and line-of-sight magnetogram (right) the location of the flare kernels is overplotted. The colours represent the time stamp from violet (the beginning) to red (the end) colours. []{data-label="fig:examples_flat"}](fig-flat.pdf){width="\textwidth"}

Let us assume that there really are three classes of WLFs and let us find what makes those classes different. By plotting the flare kernels on top of the magnetogram we found that in the most cases, these point concentrate around strong polarity inversion lines. Generally, it is expected that the flare kernels in the lower atmosphere will reside in the footprints of quasi-separatrix layers [QSL; see e.g. @1995JGR...10023443P], which is a generalisation of a too restrictive null-point configuration needed in an original formulation of the 