How do I implement Entity Reference Behaviour Plugins? Do Entity Reference behaviour plugins exist for Drupal 8? Please see:
https://www.drupal.org/node/1803064#comment-10717088 
Are there any existing examples; documentation or code?


I would like to upgrade entityreference_prepopulate but I am unsure about these behaviour plugins.
Answer on IRC via berdir: &quot;no, that doesn't exist&quot;. So it simply does not exist yet in D8.
Supplementary info provided for field settings in D8 =&gt;
berdir:

note that fields, like all config entities have a concept of third party settings. you can use that to store per-field settings. didn't check the other parts
see https://www.drupal.org/project/allowed_formats for a projects that uses third party settings on fields