Currently, sequenced segments are additive, meaning a new segment is added on each iteration, but none are every removed. eg: a[1:(g:1)][2:(f:1)] might generate ap followed by apl (for a person named Pat Lee).

However, there are use cases where segments could be replaced on iteration. So (eg) a

{1:(g:1)} {2:(f:1)}

might generate ap followed by al. For longer patterns, the two styles could be mixed.