Starting character(s) of the match key. If no filter is applied (the default), this is the starting character of the match key. If a filter is applied, this is the starting sequence of characters in the match key, beginning with the left-most character.

Number of match keys in the match key table that begins with the starting character(s). Hotspots in the match key table show up as disproportionately tall spikes (high number of match keys), relative to other characters in the histogram.