I'm interested in "addDestroyCallback" in pin behavior.
I found that each pin behavior will push a function object to runtime's "destroycallbacks" array through "addDestroyCallback". Function object array "destroycallbacks" will be executed when each object destroyed.
When pin behavior had been destroyed, the callback in "destroycallbacks" will never been removed.
If I create many many pin behaviors, these might insert many many function objects into "destroycallbacks" array and never remove it. It's not a bug, just a little ... drawback.