In AS2, you could use both onRelease and onReleaseOutside
together to ensure that you know when the mouse is released (even
if the frame rate caused it to be off a little or if the mouse was
released off of the stage).
In the AS3 migration from AS2 it says that both of those were
replaced with the mouseUp event... however if you just use mouseUp
there are some problems. Like, as mentioned above, if the user puts
the mouse off the stage and lets go, it is not registered.