Two Cursors, One Document

Part 6 of 7: Documents in the Wild

Janice and Theo are writing a chapter together, and they have a system that has failed them for years. It is called chapter_final_FINAL_v3_theo_edits.docx, and every writing pair on earth has some version of it. One person has the file. The other person waits. Or worse, both edit copies and someone spends Sunday reconciling two documents by hand, praying they did not miss a paragraph.

Sharing (Part 5) got Theo into Janice's document. This post is about what happens when they are both in it at the same time, which is a genuinely harder problem, and the one that usually breaks.

The cursor you do not recognize

Open a shared document and start typing, and the first thing you notice is presence. Anyone else editing shows up as a little colored avatar in the header, and their cursor appears in the text with their color on it. Janice writes the dialogue; Theo's caret is right there, three lines down, tightening the prose behind her. Nobody is guessing who is in the file or whether it is safe to touch. You can see them.

The document editor showing a second editor present: a colored avatar in the header next to the document controls, while the shared chapter is open

Theo's avatar, up in the header, while both of us are in the same chapter. The cursor you do not recognize is his.

Worth knowing how this is built, because it explains its limits and its virtues: presence is self-hosted and works by polling. Editors send a small heartbeat with their caret position, and pick up their peers' cursors and the document's latest version on the way back. There is no third-party real-time service in the loop. It is not a sub-100-millisecond gaming cursor; it is a steady, private "someone else is here and this is where they are" that costs you no external dependency.

The merge that keeps your words

Presence is the visible half. The half that actually saves the marriage is what happens when Janice and Theo edit overlapping text at the same moment. In most tools that is where you meet the dreaded dialog: "this document was changed elsewhere, keep your version or theirs?" One of you loses work, or you both stop and negotiate.

Documents does not ask that question. When your edits and a collaborator's edits collide, they auto-merge. Your text and your cursor position are kept, their changes fold in around yours, and you get a quiet little notice that says "Merged edits from Theo" so you know it happened. No modal, no forced choice, no losing the sentence you were mid-way through. The times I have watched this work are the times I stopped worrying about co-editing at all.

It is not magic, and I will not pretend it is. Two people rewriting the exact same sentence in the exact same second is still two people disagreeing, and no merge algorithm settles a disagreement for you. What it does is remove the mechanical fear, the "did I just overwrite you" panic, so the only thing left to sort out is the actual editorial call, which is the part humans are supposed to do anyway.

Two cursors, one document, nobody's words thrown away. That is co-writing without the version-number graveyard. Next up, the last move: taking a finished document and sending it out into the world as a public page, a post, and a list.

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