Autocomplete pops up suggestions while you type: the system chooses the moment, the position, and the shape of the suggestion, and you respond to it. Blanks invert that relationship. You type _ exactly where the response should land; the system has no say in position or timing, only in content.
Why the inversion matters
Because you place the summon character, there is nothing to dismiss and no flow interruption: no dropdown stealing keystrokes, no ghost text to escape. A _ is also on every keyboard, on every platform, in every text field, which is what lets the same primitive work in a terminal, a browser, and a CLI prompt.
Different failure modes
Autocomplete that guesses wrong costs you attention every time it fires. A blank that cannot resolve simply stays as _: visible, harmless, yours to rephrase or delete. Once a blank resolves, the result is locked against other suggestions until you edit it yourself.
Cues are the passive layer, and still non-blocking
OpenCues does have a passive direction (cues dim words that have alternatives), but the dim is a colour-channel signal layered on your text: it never moves words, never takes focus, and is fully ignorable. The design constraints are covered in the Inline Cues essay.
Related: What is a blank? · OpenCues vs chat panels · OpenCues vs Smart Compose · OpenCues vs text expanders · GitHub repo