Selecting text string in Input Text box with AS?

Would like to implement functionality for when a user changes focus to an Input Text box, the text it contains will become automatically selected and ready to copy (Ctrl-C) or overwritten.

Had tried the following to no avail (in MX 2004 Pro):

[AS]
name_txt.onSetFocus = function(oldFocus) {
Selection.setFocus(this);
Selection.setSelection(0,-1);
}
[/AS]

Is this even possible? :h: