The black region's envelope is defined by edge elements. The black envelope extends from a boundary marked by each edge to the right (+1) boundary of the propability figure. The default black range is defined by two edges:

<edge probability='0.8' confidence='0.2'/>
<edge probability='0.8' confidence='1.0'/>

The probability attribute for each edge defines its position on the probability figure ( X ) axis.

The confidence attribute for each edge defines its position on the confidence figure ( Y ) axis.

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