TIdEncoderClass = class of TIdEncoder;

TIdEncoderClass is a TIdEncoder class reference that determines the object type created when a new instance of the encoder is created. TIdEncoderClass is passed as an argument in the EncodeString function, and is used to create the internal class instance that performs the encoding operation. 

Pass TIdDecoderClass as an argument to the DecodeString function to perform decoding for a string value.