You want to use ActionScript to set the insertion point in a text field.
Selection.setSelection( ) method,
specifying the same value for the starting and ending indexes.
You can use
Selection.setSelection( ) to set the
cursor position in a text field by setting the beginning and ending
index parameters to the same value. This example sets the cursor
position in the text field that has focus:
// Positions the insertion point before the first character Selection.setSelection(0, 0);