HRI_EUV observations of the brightening on a border of dark material in an active region on 2022 April 1. The white arrows in the top panel mark the brightening location. The bottom panel shows a time–distance map along one of the jets observed propagating from the bright structure. Two kinds of brightening events can be seen: the bright edge of the dark structure oscillating up and down, and jets propagating upward (both indicated by the arrows; see Sect. 3.1.4).