folds a conditional list.
folds a conditional list. if an entry is optional, the result is split and the entry affects the result only partially
explodes an optlist.
explodes an optlist. use carefully, can be very expensive
convenience function to add an element (e) with feature expression (f) to an conditional tree (t) with the initial context (ctx)
returns the last element (which may differ in different contexts) or None if the list is empty
convenience function, zip two conditional values and map the result
convenience function, zip two conditional values and map the result
combines entries from two conditional values to a conditional pair of values
combines entries from two conditional values to a conditional pair of values
this explodes variability and may repeat values as needed
maintains a map a name may be mapped to alternative entries with different feature expressions