Expression Editor

The field is a real input, so the caret, selection, undo and screen reader editing are the browser's own; the highlighted copy behind it is aria-hidden. In one line the input is the role="combobox", with aria-expanded, aria-controls, aria-autocomplete="list" and aria-activedescendant pointing into the suggestion listbox, so focus never leaves the field: ArrowUp and ArrowDown move (and wrap), Enter or Tab inserts, Escape closes, Shift+Tab leaves without choosing, and Ctrl+Space or Alt+ArrowDown opens the list on demand. ARIA in HTML allows no role on a textarea, so the multiline field stays a textbox with the same attributes minus aria-expanded, and a status says how many suggestions there are instead. Each option's name says what it is — "price, 12" or "round, function: Rounds half away from zero" — and the active one has a bar at its start as well as a fill. An error sets aria-invalid, is underlined with a wavy line so it does not depend on colour, and its message is the field's description. The result and the error share one polite live region that only speaks while the field has focus and the list is closed, after a pause in typing, so a page of formulas recalculating does not talk over itself. Formulas are laid out left to right in every locale, because the bidi algorithm would otherwise move parentheses in a right-to-left page.