Pair features can override other pair features, which means that if a pair feature selects a pair named ap1 can override another pair feature with this pair also selected. The overridden ap1 will be marked as overridden in the Pairs list of the latter feature, and it will not add any conditions for that pair. The default pair feature is always overridden by all other pair features. Between other pair features the relationship can either be contributing or overriding just like normal features. The major difference between pair features and normal features is that the pair feature does not override the selection. Assume that two pairs named ap1  and ap2 under definitions share boundaries in, for example, the destination selection. If a pair feature selects both these pairs but another pair feature overrides ap1, the pair ap2 is still active. Both pair features then includes the shared boundaries.