The Continuity condition is suitable for pairs where the boundaries match; it prescribes that the level set variable is continuous across the pair.

A No Flow subnode is added by default and it applies to the parts of the pair boundaries where a source boundary lacks a corresponding destination boundary and vice versa. The No Flow feature can be overridden by any other boundary condition that applies to exterior boundaries. By right-clicking the Continuity node, additional Fallback feature subnodes can be added.