Add guide for custom Stimulus controllers

[falkgeist]

No description provided.

[zoglo]

Unsure if I like having this in the documentation since people don't really need to use stimulus but can use mutation observers. Especially not within the dev as it's not part of the Contao API.

[falkgeist]

I see your point.

The problem with mutation observers is, that any changes to the DOM based on the observers might in turn trigger Stimulus' observer 🤪. But that is a different issue, imho.

The issue described in the first paragraph is very real though, if you ask me:

Custom backend JS with listeners to the DOMContentLoaded event is only triggered on 'real' page loads, not Turbo navigation.

Implementing your own controller is not the definitive fix for that (there's your mentioned mutation observers or also Turbo events), but it does mitigate the issue.