and attempts based on an extrapolation of the trend of the increasing Ly$\alpha$ fraction seen at lower redshifts found a reverse of the trend, showing only 20%–30% of faint galaxies with Ly$\alpha$ emission [e.g., @fontana10; @pentericci11; @ono12; @schenker12; @finkelstein13; @pentericci14]. This steep decrease beyond $z \sim 6$ is in line with measurements of Gunn–Peterson troughs [@gunn65] in the spectra of distant quasars [@fan06], which signal the (near) completion of reionization by $z \sim 6$.

Several attempts have been made to interpret the observed drop in the Ly$\alpha$ fraction in connection with the neutral fraction of the IGM or different models of reionization. Earlier works suggested, assuming that the observed drop in the Ly$\alpha$ fraction from $z \sim 6$ to $z \sim 7$ is entirely driven by the change in the IGM transmission, that it requires a steep increase in the volume-averaged neutral fraction of $\Delta x_{\rm H\,{\sc I}}>$ 0.4–0.5 over $\Delta z=1$ [@dijkstra11; @pentericci11]. Alternatives have subsequently been proposed that account for the possibility of other sources of Ly$\alpha$ attenuation which alleviate the amount of the required increase in the neutral fraction. For example, @dijkstra14 suggested that the change in the intrinsic physical properties of galaxies such as an increase 