s = string.Format("{0}", arg0, arg1); // Noncompliant, arg1 is declared but not used.
s = string.Format("{0} {2}", arg0, arg1, arg2); // Noncompliant, the format item with index 1 is missing so arg1 will not be used.
s = string.Format("foo"); // Noncompliant, there is no need to use string.Format here.