Hi,
First of all, thanks for this library. I really love the concept and it is a nice, logical extensions of custom elements.
However, I found that the behaviors do not work if the element is added before the library load. The scripts we are using are automatically added as "defer" scripts to load in a non-blocking way (we do not have control over the loading mechanism of the scripts).
Is this a known issue of the library? Unfortunately if that's the case I likely won't be able to use the library, but I hope this will give some ideas to browser implementers :).