Inline autocomplete

Inline autocomplete puts the guess where the typing is. The field shows the whole candidate, the part the reader typed followed by the part the field supplied, and the supplied part is selected. That selection is the entire mechanism, not decoration. Because the remainder is a selected range, the next character typed replaces it rather than landing after it, so a reader who ignores the guess never has to delete it; and because it is still a range, one press of the right arrow or End collapses the selection and accepts the completion as text. Typing forward or typing over are the same gesture, which is why the pattern survives fast typists at all.

It is old, and the browser address bar is where most people meet it. The ARIA authoring practices treat it as a property of a combobox rather than a pattern of its own, naming the inline half “list with inline completion” when a popup list is showing at the same time, and requiring that the completion be a selected range so assistive technology reports the field’s value honestly. The failure mode it exists to avoid is the field that inserts the remainder as ordinary text: the reader keeps typing, the letters go after the guess, and the value becomes a collision of two words that neither party asked for.

There is a name collision worth being precise about, because it has arrived recently and loudly. This entry claims the classic reading: a completion drawn from a known finite set (your contacts, your history, a list of countries), inserted into the field, selected. It is not the AI suggestion that shows a whole predicted phrase in grey after the cursor and waits for Tab. That thing is also called ghost text, and it differs in three ways that matter to the reader: it is generated rather than looked up, so it can be wrong in ways a list cannot; it is unselected inert text, so a keystroke does not overwrite it; and it is accepted with Tab rather than by continuing to type. Both are worth having. Calling them the same word makes it impossible to say which one a field is doing, so this site keeps “inline autocomplete” for the selected-remainder sense.

The near neighbours are worth keeping apart too. Typeahead is the field that searches while you type, showing results elsewhere, and needs no completion in the field at all. Mention autocomplete triggers on a character inside prose and inserts a token rather than letters. Inline autocomplete is the narrow case where the guess lives in the value, and the selection is the promise that it is only a guess.