An emotional relationship line between two people.

Fields:

• :pair — a {id_a, id_b} tuple of the two people the bond connects.
• :type — one of :close, :distant, :conflict, :hostile, :cutoff, :fused.

Bonds are drawn as non-structural lines (they never change the generational layout) and are coloured and styled by :type: closeness in green, distance and cutoff dashed, conflict and hostility in red.