The declared parameter that the argument at argIndex fills, walking the parameters as a call
spells them out: a plain parameter is one position, and a rest parameter or repeating group cycles
through its slots from where it starts.
Parameters
params: readonlyIParameterType[]
argIndex: number
Returns IParameterType|null
null for a negative index, or one past the last parameter of a declaration with no rest
parameter or group.
Remarks
A parameter declared AFTER a group (SWITCH's default) is never the answer: a position alone
cannot say where the repetitions end, so the group keeps it — as the signature does.
The declared parameter that the argument at
argIndexfills, walking the parameters as a call spells them out: a plain parameter is one position, and a rest parameter or repeating group cycles through its slots from where it starts.