Feature Request: Supported code notification message on Custom HTML Block

[chekle]

What

Please consider adding a notification/warning message about incompatible code: https://wordpress.com/support/wordpress-editor/blocks/custom-html-block/#supported-code to the Custom HTML Block.

For example, if the user doesn't have a plugin-enabled plan, please display a warning message if they try to insert an embed, frame, iframe, form, input, object, textarea, script, style, or link tag into the Custom HTML Block.

We explain this in our documentation, but some users are left very confused as to why their code doesn't work.

In this interaction, 9707932-zd-a8c, a user reported that their custom HTML code previews correctly but appears wrong when published. We found that some tags they used (like <script>) require a Business or Commerce plan and were being stripped.

Why

I believe adding a warning message about unsupported code for users on non-plugin-enabled plans will reduce the confusion when their code doesn't work as expected, help reduce support volume, and improve the usability of the Custom HTML Block.

How

If a user on a non-plugin-enabled plan includes any of the following (embed, frame, iframe, form, input, object, textarea, script, style, or link tag) in the Custom HTML Block, they should see a message display about supported code, and a link to visit for more information (https://wordpress.com/support/wordpress-editor/blocks/custom-html-block/#supported-code)