[dev-v5][Docs] Add placeholder autofill docs from v4

[MarvinKlein1508]

Pull Request

📖 Description

This PR adds the missing placeholder autofill docs from v4.

👩‍💻 Reviewer Notes

Not sure about the position where I put the actual markdown file. Maybe we wanna have a shared folder?

✅ Checklist

General

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Component-specific

• I have added a new component
• I have added Unit Tests for my new component
• I have modified an existing component
• I have validated the Unit Tests for an existing component

⏭ Next Steps

This docs needs to be added to the FluentAutocomplete docs as well.

[dvoituron]

I asked to Copilot and his answer is here. So, do we need to explain the default HTML behaviors? To discuss.

---

The behavior you describe applies to native HTML elements as well.
Browsers use heuristics to decide when to show autofill suggestions, and those heuristics are not limited to autocomplete. Placeholder text is one of the signals that can influence autofill.

• placeholder text can influence autofill
• autocomplete="off" is not reliable
• Avoid semantic placeholder values if autofill is undesired
• Disabling autofill requires browser-level user settings, not HTML

Source:

• https://css-tricks.com/almanac/pseudo-selectors/a/autofill/
• https://www.w3tutorials.net/blog/how-does-form-auto-filling-in-the-browser-work/
• https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/:autofill
• https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/Turning_off_form_autocompletion
• https://www.microsoft.com/edge/features/autofill

[vnbaaij]

Agreed. No need to explain that here

[MarvinKlein1508]

I think it's good to have as this can save us some issues getting raised. I remember that we spent quite some time on figuring this one out.

See #3899 even javiercn had to do some research on this dotnet/aspnetcore#62296

Having it in the docs also means we have this details in the MCP server :)

[dvoituron]

I’m not opposed to adding this information to clarify things for certain developers. My only other suggestion, then, is to place the PlaceholderAutofill.md file in the TextInput folder, which is more appropriate, to avoid putting it in the root of Components. And rename it to ChapterPlaceholderAutofill.md or SectionPlaceholderAutofill.md to clarify this is not a page.

[MarvinKlein1508]

Yes. I placed it on the root as the same concept applies for FluentCombobox and FluentAutocomplete. What if we add a Shared folder in the root which holds this kind of docs.

[vnbaaij]

Agreed. No need to explain that here