Coda’s pattern is very close to Google Docs but adapted to a block/document app. The selected text stays visually connected to the comment, while the actual discussion lives outside the writing flow. That keeps the document clean.

The interaction is also discoverable because the comment button appears in the same place as formatting actions. The user does not need to know a shortcut or open a sidebar first.

The best part is the dual anchoring:

inline highlight on the text

floating/sidebar comment card aligned nearby

That gives users both local context and thread visibility.

The composer also feels lightweight: it does not open a modal, does not move the page, and does not interrupt editing too much.

The comment action is hidden until text selection, so users may not discover it unless they already expect it.

Also, the comment card sits in the right margin, which works well on desktop but may become harder on narrow layouts. For Seed, you’d need a mobile/narrow-window behavior: popover, bottom sheet, or comments panel.

Coda uses a “selection toolbar → anchored margin thread” pattern.
It treats comments as annotations on text ranges, not as block-level discussions. The UX is strong because the comment is created from the same interaction surface as formatting, while resolved/ongoing discussion lives outside the document body.

I’d mark this as a strong candidate pattern:

Use this for Seed if you want comments to feel like lightweight document review, not like heavy discussions.

Key ideas to borrow:

selected text becomes persistent highlight

comment composer appears near the range

thread lives outside the text flow

clicking either highlight or thread reconnects both

keep creation inside the normal text-selection toolbar