I don't have one on Ellie, but Ellie itself has a nice example with how it wraps CodeMirror (https://github.com/ellie-app/ellie/blob/master/assets/src/El...)

I don't know if there is a formal name for this pattern, but we've been calling in the "un-attr" pattern, you define an opaque type like

  type Attribute msg
      = Attr (Html.Attribute msg)

And then expose functions that allow you to set attributes you whitelist. In the JS you use setters to hook into when the attribute changes and respond to it (https://github.com/ellie-app/ellie/blob/master/assets/src/El...)