AGN optical classification of X-ray AGN in clusters (black circles for broad-line and red squares for narrow-line AGN) compared to the control sample of field X-ray AGN (dashed black line for broad-line and continuous red line for narrow-line AGN). The classification and detailed results are described in Sect. 3.2.1 and Sect. 4.2.1. Error bars and shaded areas indicate the 1σ confidence limits for small numbers of events (Gehrels 1986).