Flash MX 2004.
compiledClipInstance.description
Property; a string that is equivalent to the Description field in the Accessibility panel. The description is read by the screen reader.
The following example illustrates getting and setting the description property:
// Get the description of the current selection.
var theDescription = fl.getDocumentDOM().selection[0].description;
// Set the description of the current selection.
fl.getDocumentDOM().selection[0].description =
"This is compiled clip number 1";