completionwindow

A completion window is a user interface element that presents a list of possible text completions for the partially typed input. It is commonly used in text editors, integrated development environments, command shells, and search boxes to speed input, reduce keystrokes, and help users discover valid tokens or commands.

Typically, the completion window appears as a pop-up anchored near the text caret or input field. It dynamically filters its items as the user types, showing only those that match the current prefix. Users navigate the list with keyboard arrows, and selections are inserted into the input when confirmed with keys such as Enter, Tab, or a mouse click. Some systems support additional features such as fuzzy matching, case sensitivity options, and inline hints.

Data shown in a completion window comes from various sources, including language syntax and symbol dictionaries in code editors, command or file name histories, project symbol indexes, or user-defined dictionaries. Triggers for display may be automatic after a minimum prefix length or explicit through a command or shortcut.

Variants include separate drop-down completion windows and inline suggestions, where a ghosted or underscored hint appears within the input field rather than a separate list. Accessibility considerations emphasize keyboard-only navigation and screen reader compatibility, while performance concerns focus on responsive filtering, debouncing, and asynchronous data retrieval.

See also: autocomplete, intelligent code completion, fuzzy matching, inline hints, symbol completion, lookup, and related concepts in user interface design.