Flash MX 2004.
symbolInstance.description
Property; a string that is equivalent to the Description field in the Accessibility panel. The description is read by the screen reader. This property is not available for graphic symbols.
The following example stores the value for the Accessibility panel description of the object in the theDescription variable :
var theDescription = fl.getDocumentDOM().selection[0].description;
The following example sets the value for the Accessibility panel description to Click the home button to go to home:
fl.getDocumentDOM().selection[0].description= "Click the home button to go to home";