Post Content: Add some text to the Post Content block when used in a 404 context

[scruffian]

Description

Similarly to #33515, we should output some default copy on the page when the post content block is used in a 404 context. This makes the creation of 404 templates much simpler as themes can simply use the same template as their index.

How has this been tested?

• Add a post content block to a 404 template
• Confirm that you see the text "It looks like nothing was found at this location.".

Another benefit of this approach is that the default text can be translated. We might want to change the copy.

Screenshots

Types of changes

New feature (non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[ntsekouras]

👋 - I don't think we should be adding hardcoded content like that. Such content should be editable and removable. Even if we added a wrapper with a css class here, someone would have to use css to hide it.

In my head this is something to be handled in 404 template but it seems I can't understand how this is not working. For example right now that we have a 404 template in tt1-blocks with a custom header block - we can't make this translatable?

[scruffian]

We don't have any way to translate content in the HTML files for block templates, or block template parts. I've made some other suggestions for how we might work around the problem:
#33192
#33217

[mcsf]

Regardless of the outcome of those PRs (I'm betting on #33217), this feels best absorbed by patterns than by hard-coded server-side logic.

[scruffian]

Even if the patterns PR merges, I think this is a very useful tool. If I want to create a simple site with only one template, this allows me to do that...

[mcsf]

If I want to create a simple site with only one template

I think this is a good aspiration for FSE. Building simple sites should feel as convenient as working with a single template. But I think the current proposal is overloading base FSE blocks with meaning and hardcoded decisions.

[carolinan]

I disagree with the approach because I think users should be able to change everything on the 404 template by editing the template.
Theme authors can still filter the content if it is a 404 page.

FSE themes don't have conditionals in the same way as classic PHP based themes do, if we want to implement that, then that needs to be a complete system, not a one off for the 404 page.