Constant COINCIDENT_OPERANDS 

pub const COINCIDENT_OPERANDS: &str = "operand faces read as one surface within tolerance";

The DeviationContribution::detail of a boolean measured against an exact result in which faces of the two operands were read as one surface within tolerance (#324: a niche’s inner cylinder a unit in the last place off a curved wall’s inner face): its bound is the furthest that reading moved an operand, so the exact result the mesh is measured against is the boolean of operands perturbed by at most that much (ADR 0080). It names the perturbation, as SNAPPED_OPERANDS does; the boolean’s own contribution bounds the mesh’s distance to that result.