That's a great idea.

Technically, there are many APIs that allow us to intervene in the editor to display warnings: in the list view, in the block toolbar, in an overlay above a block, in the sidebar, etc.

If someone wants to whip up a lightweight plugin for this, happy to see that done :) (Either as a plugin on w.org/plugins, or stand alone for wporg).

As I said on Slack: ​https://wordpress.slack.com/archives/C02RP4WU5/p1765856008439419?thread_ts=1765855859.923399&cid=C02RP4WU5

Here’s an example of what I was thinking of doing.. does anyone have any thoughts on a better way to do it? I’m not really great at editor enhancements, but I’m sure I could force a CSS style in to make externally-loaded images look ugly in the editor :)

Closes: https://meta.trac.wordpress.org/ticket/8149

This PR adds a plugin that displays a warning for blocks that contain inappropriate external resources. This helps encourage contributors to upload resources when creating documentation by copying content from external documents, preventing media from potentially disappearing in the future.

## How this plugin works

• Check the three blocks Image, Cover, and Video that allow you to set external resources as media.
• Check whether the media URL matches your site's domain. If not, this plugin checks whether it matches one of the allowed domains. Finally, if the media URL does not match any domain, it is considered an inappropriate media resource.
• Blocks with invalid media resources will have a red border and overlay.

Additionally, the block toolbar will have a red icon button. Clicking that button will display a popover with details about the error.

## Testing Instructions

Use the .wp-env.override.json file to map the plugin to your local wp-env environment:

{
	"plugins": [
		"./your/plugins/plugin",
		"../path/to/wordpress.org/wordpress.org/public_html/wp-content/plugins/wporg-media-resource-checker"
	]
}

## Screenshot