Document attribute-based discovery in the handbook

Adding this to the meta issue about the conversion (which I think would be a better parent for this, but don't want to just change that).

We need to ensure we document the outcome of 🐛 AttributeClassDiscovery fails while trying to include non valid plugin class Fixed , as there are stricter rules for what can exist in the namespace for pure attribute discovery compared to annotations.

There is an existing page for ' Drupal Plugin Discovery → ' which lists four methods, StaticDiscovery, HookDiscovery, AnnotatedClassDiscovery and YamlDiscovery. That seems like a suitable place to add 'Attribute discovery'. Would that work?

Added a page for attribute plugins, which is basic and needs work, https://www.drupal.org/docs/drupal-apis/plugin-api/attribute-based-plugins →

What more needs to be done here?

Can this be closed per #6?

I think we should extend the page to include "Using attributes in your own plugin type" similar to the annotations example at https://www.drupal.org/docs/drupal-apis/plugin-api/annotations-based-plu... →

Started the section, Using attributes in your own plugin type → .

Reviewing just the section mentioned in #11 change makes sense based on reviews of the attribute tickets.

But question on "Defining a plugin" section.

a key for an optional deriver class

we've been requiring that for attributes so should optional be removed. Either way seemed out of scope for this ticket so maybe a follow up.

The deriver class is optional, the key is not.

I added another page, Create a custom attribute class → . And that states that the deriver key is required in the Attribute class.

I think this is good progress, and we can refine it as time goes on. Eventually we'll need to deprecate and retire the annotations documentation but need to deprecate annotations first and that's still quite far off.

Automatically closed - issue fixed for 2 weeks with no activity.