Angular attributes produce HTML validation errors

[johnnygerard]

Which @angular/* package(s) are the source of the bug?

Don't known / other

Is this a regression?

No

Description

Angular uses non standard attributes which produce HTML validation errors such as:

• Attribute _ngcontent-ng-c3135559882 not allowed on element input at this point.
• Attribute ng-reflect-model not allowed on element input at this point.

Why not use data-* attributes?

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

No response

Please provide the environment you discovered this bug in (run ng version)

No response

Anything else?

No response

[JoostK]

There have been numerous issues around this, e.g. #15891 and #25355, with #40595 as an attempt to change the _ngcontent attributes into data attributes. Note that ng-reflect attributes are dev-only.

With the rise of SSR I can see some point of addressing it, but this may not just be a matter of changing the attribute names due to potential breakages.

[JoostK]

Labeling as "server" since this should only be relevant for SSR, as normally only the DOM has these attributes.

[johnnygerard]

My issue is not about SSR but really about HTML validation.

The argument I read in your mentioned issues is that HTML validation does not apply to the DOM, but only the source HTML.

If we agree that valid HTML is desirable, even for an Angular application, then the question becomes:
How to best validate the Angular templates?