MSC4159: Remove the deprecated name attribute on HTML anchor elements (#4159)

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>

proposals/4159-remove-anchor-name.md

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+# MSC4159: Remove the deprecated name attribute on HTML anchor elements
+
+Some message types in `m.room.message`, such as `m.text`, permit including HTML in the event content.
+The spec [recommends] that clients limit the HTML they render to prevent attacks and provides a list
+of permitted HTML tags and attributes. In particular, it allows using the `name` attribute on `a` tags.
+This attribute is obsolete according to the [WHATWG HTML Living Standard] which is why this proposal
+attempts to remove it from the spec.
+
+
+## Proposal
+
+The `name` attribute was originally introduced to define targets for linking to specific parts of a
+webpage. As an example, including the named anchor `<a name="foo">bar</a>` on a site allows you to append
+the fragment `#foo` to the URL to cause your browser to scroll the anchor into view after loading the page.
+
+In modern versions of HTML this feature has been superseded by the `id` attribute which extends targeted
+linking to more than just `a` tags. As a result, the `name` attribute is marked deprecated in [MDN].
+
+> Was required to define a possible target location in a page. In HTML 4.01, `id` and `name` could
+> both be used on `<a>`, as long as they had identical values.
+>
+> Note: Use the global attribute `id` instead.
+
+Furthermore, it is also tracked as [obsolete but conforming] in WHATWG.
+
+> Authors should not specify the `name` attribute on `a` elements. If the attribute is present, its value
+> must not be the empty string and must neither be equal to the value of any of the IDs in the element's
+> tree other than the element's own ID, if any, nor be equal to the value of any of the other `name`
+> attributes on `a` elements in the element's tree. If this attribute is present and the element has an ID,
+> then the attribute's value must be equal to the element's ID. In earlier versions of the language, this
+> attribute was intended as a way to specify possible targets for fragments in URLs. The `id` attribute
+> should be used instead.
+
+On top of the deprecation of the `name` attribute in HTML, it is unclear what this feature would ever have
+been used for in the context of Matrix. It appears highly undesirable to let events define targeted links
+into a client's UI, not least because the value of the `name` attribute would need to be unique on the
+entire page. Additionally, linking to specific events is already possible via [matrix.to URIs].
+
+Therefore, the `name` attributed is removed from the list of permitted attributes on `a` tags without a
+replacement.
+
+
+## Potential issues
+
+Use cases that currently depend on the `name` attribute will be broken once the attribute is removed from
+the allowed list. No concrete use cases are known as of writing, however.
+
+
+## Alternatives
+
+None.
+
+
+## Security considerations
+
+None.
+
+
+## Unstable prefix
+
+None.
+
+
+## Dependencies
+
+None.
+
+
+[MDN]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#name
+[WHATWG HTML Living Standard]: https://html.spec.whatwg.org/
+[matrix.to URIs]: https://spec.matrix.org/v1.10/appendices/#matrixto-navigation
+[obsolete but conforming]: https://html.spec.whatwg.org/#obsolete-but-conforming-features
+[recommends]: https://spec.matrix.org/v1.10/client-server-api/#mroommessage-msgtypes