EIdReplyRFCError = class(EIdReplyError);

EIdReplyRFCError is an EIdReplyError descendant that represents the generic exception raised for RFC-compliant protocol responses. 

EIdReplyRFCError implements an ErrorCode property for the protocol response, and an alternate cosntructor for creating the exception with a given error code and message text. 

EIdReplyRFCError is used as an ancestor class for protocol-specific errors, like EIdHTTPProtcolException, EIdNNTPConnectionRefused, and EIdSMTPREplyError.