Disabling focus (editing) of a text field

AS v2:
When the user clicks outside a textfield on stage (named showNotes), I don't want the textfield to be editable anymore.

I have tried to set the focus to another text field, but it doesn't work:

PHP Code:

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onClipEvent (mouseDown) {
_root.createTextField("myTF", 120, 50, 50, 10, 10);
_root.myTF.type="input";
_root.myTF.text=" "; //a SPACE or temp "foo" text, but NOT empty !
_root.myTF.stage.focus = myTF; myTF.setSelection(myTF.length,myTF.length);
Selection.setFocus("_root.myTF");
_root.myTF.text = "";
showNotes.selectable = false;
} 


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Also tried:

PHP Code:

---

stage.focus = null; 


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Please help.

(edit) Ps: changing the selectable property of the text field disables the blinking | coursor, but the user can still write in it.