String Message that includes "placeholders" where elements from argumentList are to be inserted. The message can contain any sequence of characters. Use the {n} placeholder to insert elements from argumentList, where n is the index of the element that you want to insert. For example, the following pattern string inserts elements 0 and 1 into the message:

String List Optional. List of strings to use to populate pattern. If argumentList is not supplied, the service will not replace placeholders in pattern with actual values.

String Result from substituting argumentList into pattern. If pattern is empty or null, this parameter is null.