Any TOS ThinkScript expert here?

csw2002

TOS Thinkscript is notorious for its lack of documentation. I am currently stuck on how recursion works in ThinkScript and in particular how compoundValue is used for recursion initialisation. The help file in TOS ThinkScript editor states that

compoundValue(int length, IDataHolder visible data, IDataHolder historical data)

length  default value: 1

Calculates compound value that is equal to 'historical data'(if bar number is less than 'length') or 'visible data' expressions calculations. It is used to initialize studies with recursion.

Usage in:

  HeikinAshiDiff; ReverseEngineeringRSI; CyberCyclesOscillator; VariableMA; RelativeStrength; PositiveVolumeIndex; NegativeVolumeIndex; MovAvgAdaptive;

Any idea what it means? I am a fairly competent programmer but I am very stuck on TOS ThinkScript right now.