Autocomplete widgets can be helpful for accessibility because they can make it easier to enter text by providing suggestions based on the characters initially typed. This particularly helps people who find typing more difficult and people who may be susceptible to spelling mistakes.
Creating an accessible integrated autocomplete widget is a complex process. You need to ensure that screen-reader users are notified when the list of suggestions appears and that they can enter the list and select an option...
Modal dialogs can enhance usability by focusing attention on a specific message that requires a user action to continue.