Step 1: rollOver
MovieClip.prototype.hasOwnProperty('enabled'): true
button.hasOwnProperty('enabled'): false
'enabled' in button: true
button.enabled: true
// button.enabled = undefined
button.hasOwnProperty('enabled'): true
'enabled' in button: true
`button.enabled` is now a falsy value.
`button.enabled` is undefined.

Step 2: press
`button.enabled` is still a falsy value.
`button.enabled` is still undefined.

Step 3: release
// delete button.enabled
button.hasOwnProperty('enabled'): false
'enabled' in button: true
`button.enabled` is now true.

Step 4: press

