Consistently designating a Sprite's hitArea helps with mouse event ambiguity. There's some catch to the mouseEnabled prop because the hit sprite will be a child. See official docs.

The callback will have an event.target that can be Class checked against with is, but as far as I can tell that assumes the 1-class-per-file idea has been taken seriously. If not, the Class being checked will not exist.

function over(event) {
  // if ( !(event.target is Foo) ) return;
  class_name = getQualifiedClassName(event.target);
  attempt = class_name.split('::')[1];
  if (attempt != 'Foo') return;
  ...
Class checking in the habit of adding non-packaged classes into existing document class files.

At some point I'll give up listing default arguments for class constructors, and just pass a {k:v}.

AS3 could use a good html text util, though a fitting implementation might always be a unique one.