The Mask info node provides the minimum and maximum values (between 0 and 1) of a mask.
To add an Mask info node, select Edit in the main menu or right-click in the Graph Editor and select Create Node > Calculation > Mask info.
The Mask info node has no parameters.
To know the minimum and maximum values of a mask, it must be calculated completely. The nodes downstream cannot be calculated until the upstream masks has been fully calculated, which can take time.