Pops one item and transform it into a string.
For strings, this action has no effect.
For numbers, it works as expected, it transforms them in a string (see the sprintf(3C) manual pages).
For a user defined object, the method named
toString() is called.
This is similar to a Cast Object operation, although it is available in version 5 and obviously it only works for strings. It is most certainly preferable to use a Cast Object operation since version 7.