Google has announced that the real-time collaborative commenting feature in its Sheets, Slides, and Docs productivity apps is now also available on mobile. You can now instantly add a comment using the comment bubble present on the right side of a doc.
To add a new team-mate to an ongoing conversation, you just have to type their name in the comment. If the person in question doesn't have the access to the document, you'll be prompted to give them the access, following which they'll be notified about their inclusion in the conversation.
The rich commenting feature is now available to users of both iOS and Android mobile operating systems.