A MultiCurve is a one-dimensional geometry.

A MultiCurve is simple if and only if all of its elements are simple; the only intersections between any two elements occur at points that are on the boundaries of both elements.

A MultiCurve boundary is obtained by applying the “mod 2 union rule” (also known as the “odd-even rule”): A point is in the boundary of a MultiCurve if it is in the boundaries of an odd number of MultiCurve elements.

A MultiCurve is closed if all of its elements are closed.

The boundary of a closed MultiCurve is always empty.