Kinematically allowed regions for afterglow variability in the Δf/f vs. Δt/t_pk plane. Coloured lines with arrows represent the permitted regions for density fluctuations on-axis (blue), density fluctuations off-axis (red), multiple density fluctuations off-axis (green), refreshed shocks (pink), and patchy shell (black). (See Ioka et al. 2005; Chincarini et al. 2010; Bernardini et al. 2011, for details.) In this plot we show early-time (t_pk ≲ 1 ks, grey points) and late-time (t_pk ≳ 1 ks, magenta squares) flares. The red triangles are the three flaring episodes in GRB 140515A. The error bars account for the uncertainty on the behaviour of the underlying continuum: the lower bar corresponds to a flat power-law decay after 10³ s, the high bar to a flat decay normalised to the last datapoint, and the central value to a power-law decay consistent with the slope of the optical light curve after 10³ s.