The system function $sformatfbehaves like $sformat except that the string result is passed back as the function result value for $sformatf, not placed in the first argument as for $sformat.
Some more expansion:
Concatenation: Each operand can be a string literal or an expression of string type. If all the operands are string literals the expression shall behave as a concatenation of integral values; if the result of such a concatenation is used in an expression involving string types then it shall be implicitly converted to string type. If at least one operand is an expression of string type, then any operands that are string literals shall be converted to string type before the concatenation is performed, and the result of the concatenation shall be of string type.
exp. {Str1,Str2,…,Strn}