Why? If you wanted to use a behavior to replace or add to an existing DG handler, you would not be able to without this mod. You could always put the code in the DG group itself, but then you would need to duplicate it for each DG that you wanted to use the same code. You could chain it to the end (after the library code), but then it would impact every DG in the app (which may or may not be an issue).
https://github.com/bwmilby/lc-misc/tree ... DGBehavior

The README on GitHub also links to the discussion thread, the PR, and the bug report.