While a discussion broke out years ago around a commenting API, this issue seeks to be a gathering place on what in line commenting could look like today as phase 3 has previously been more firmly announced and early explorations begin. In particular, this area of work is listed as a task for real time collaboration and this issue can act as a gathering place for coordinating what's needed. To pull from this workflows post:

Introduce inline comments on blocks within the editor experience. Explore using comment types to store them. Allow marking comments as resolved. Status of comments also need to fold within individual revisions, so that it’s easy to see what specific edit state a comment refers to. Possible connection with “pending review” functionality.

Mockups

Some initial work is underway in #60622, where the following mockups were pulled from.

Adding comments:

"Add comment" is present in the block toolbar's "More" menu, in the first group.

Separately, this menu can itself benefit from migrating to DropdownMenuV2 so it can have flyouts, that might offer a better hierarchy.

Indicators:

In this example, comments have been added to a post. That makes the sidebar button appear. Implicitly that means, the comments button only appears if a post has comments.

Shown also, one of the blocks selected, with indication in the block toolbar: a stack of avatars of who interacted with this particular block. This particular design is similar to past concept art for collaborative editing, which imagines a similar stack of avatars with colored rings, in the top toolbar.

The block-highlight is block-level, to start, and shows the full block except for text blocks, where the full text is highlighted even if in inline style. An alternative is a block-level highlight treatment for all blocks:

This might get too close to block level multi-select, though, so the particular visual for highlighting blocks we can refine, it can also be borders and/or underlines.

Sidebar:

The sidebar has a partially-inline visual style, but it's mainly a matter of applying the site background-color as background to the sidebar panel.

Figma.

Issue updated Aug 29.