The actor is working on something and the way to act on it is to instruct rather than to touch: in language, in commands, in a request rather than a gesture. Held in one stream, the work fragments across the acts that changed it and scrolls away between them, so reading the current state means reassembling it from a history.
A steering surface separates the two. The work sits on its own surface and holds still. The acts on it accumulate on another surface beside it — a record of what was asked, which drives the work rather than displaying it.
Coupling the two surfaces
Coordinated views applies here, and applying it is worth doing: a turn linked to the version it produced, a command linked to the change it made, designating one and having the other mark itself. Nothing about the surfaces being different kinds prevents this — a map and a table are different kinds too.
What it cannot reach is the part that does not correspond. The two surfaces are not two renderings of one model; they overlap on the work. Much of the instruction surface has no counterpart in the work — questions, rejected options, talk about something else — and changes arrive that were never discussed. Coupling can only join the overlap.
The residue also behaves the opposite way to a stale view. Coordinated views treats divergence as a defect, fixed by propagating faster or by greying the view out until it catches up. Here past instructions should not update when the work changes: they record what was asked at the time, not what exists now. A change made by hand correctly leaves no trace on the instruction side.
So the decision this pattern owns is what happens at the gap — whether the instruction surface is told about changes it did not cause, and which surface an actor is meant to read as the truth.
Instances
- a chat pane beside a document or canvas the conversation is writing
- a chat pane beside a file tree, acting on the files
- a REPL beside the editor whose buffer it evaluates
- a terminal beside the file it operates on
- a properties panel or inspector beside the canvas it configures
- a formula bar beside the sheet
The last three are the older cases and they show the move is not conversational by nature. What conversation adds is that the instruction surface is also a record of intent, which is what makes the divergence matter.
Consequences
- the work holds still on a surface of its own while the acts on it accumulate on another, so the current state is read in one place and the history of how it got there in the other
- two surfaces now claim the truth: the instruction surface records what was asked and agreed, the work itself records what actually happened, and a change made directly on the work does not narrate itself back into the instructions
- the two surfaces overlap on the work rather than rendering it twice, so only what both of them name can be coupled; the rest — talk with no counterpart in the work, changes made with no turn behind them — is a residue the design has to decide what to do with
- the arrangement spends a permanent split of the screen, and the split has a direction: whichever surface is given the room is the one the design says the work happens on
Appears in
Delegating work
- Receiving the result, step 2 — within Move the result out of the conversation: the conversation continues beside the result and controls it, and the two can come to disagree about what was decided
Related patterns
Enacts
- Agency — the actor steers from a surface of their own rather than working inside the work's own arrangement
Complements
- Extraction — extraction gives the extracted thing a surface of its own, which is what a separate instruction surface can then act on
- Coordinated views — coupling reaches whatever the two surfaces both name — a turn and the version it produced — but the surfaces overlap on the work rather than rendering it twice, so what falls outside the overlap cannot be propagated and is not stale, it is a record
Related to
- Conversation — dialogue is the usual instruction surface, though not the only one
- Editing in place — the direct route onto the work, which is where the two surfaces come apart — a hand edit leaves no trace on the instruction side
- Change review — what the instruction surface can show of a change it caused, when the change landed on content it does not display