Looks like media in wysiwyg can't be captioned like images can.
Should the caption be stored in wysiwyg or in the media?
https://drupal.stackexchange.com/questions/305844/how-to-add-captions-to-media-library-items
TODO: Document media caption options.
Modules
https://www.drupal.org/project/image_field_caption
https://www.drupal.org/project/entity_reference_media
> Modify/Add a Caption to a Media item and change it OUTSIDE of the Media item and not inside of it.
Project
Modules
Task type