The combobox pattern covers search-as-you-type fields, autocomplete address inputs, and searchable dropdowns, combining a text input with a popup listbox of options. It requires specific ARIA roles and states, including aria-expanded on the input and aria-activedescendant to track which suggestion is currently highlighted, plus full arrow-key and Enter-key support.
Custom-built comboboxes are one of the hardest ARIA patterns to implement correctly and one of the most frequently broken in audits, since minor deviations from the spec can leave screen reader users unable to tell which suggestion, if any, is currently highlighted.