FormattedReply is a TStrings property that represents the formatted text to use for the numeric reply code. 

Reading the value in FormattedReply property results in any existing values being cleared, and the text content being regenerated from the internal reply text for the collection item. If the internal reply contains the numeric code for the reply, its text is asssigned to the Text property. 

The write access specifier for the FormattedReply property is declared as an abstract virtual method, and must be overridden in a descendant class to implement the specifics of setting the value for the property.

TIdReplyRFC.FormattedReply