If the string f_target is the empty string, then the next actions apply to the main movie.
Otherwise it is the name of a Sprite and the followings actions apply to that Sprite only.
In order to use a dynamic name for the target, use Set Target (dynamic) instead.
Note that this action should not be used since SWF version 5 where you can instead access the movie members (i.e. view Sprites as objects with data members and functions.) For instance, to call the play() function on a Sprite, one can use this code:
push data 0; push data "this"; get variable; push data "_parent"; get member; push data "play"; call method;
This is equivalent to: this._parent.play(), or a Set Target of the parent object and a Play action.