Flash MX 2004.
symbolInstance.tabIndex
Property; an integer that is equivalent to the Tab index field in the Accessibility panel. Creates a tab order in which objects are accessed when the user presses the Tab key. This property is not available for graphic symbols.
The following example sets the tabIndex property of the mySymbol object to 3 and displays that value in the Output panel:
var mySymbol = fl.getDocumentDOM().selection[0];
mySymbol.tabIndex = 3;
fl.trace(mySymbol.tabIndex);