| {s1,s2,...,sn} | use s1 through sn; then use defaults |
| {{c}} | use c in all cases |
| {{c1,c2}} | alternate between c1 and c2 |
| {{c1,c2,...}} | cycle through all ci |
| {s,{c}} | use s, then repeatedly use c |
| {s1,{c},sn} | use s1, then repeatedly use c, but use sn at the end |
| {s1,s2,...,{c1, c2, ... }, sm, ... , sn} |
| | use the first sequence of si at the beginning, then cyclically use the ci, then use the last sequence of si at the end |
| {s1,s2,...,{},sm,...,sn} | use the first sequence of si at the beginning and the last sequence at the end |
| {i1->v1,i2->v2,...} | specify what to use at positions ik |
| {spec,rules} | use rules to override specifications in spec |