applicationdefined

Applicationdefined is a term used to describe elements of a software system that are defined by the application rather than by the operating system, framework, or standard libraries. It denotes customization and extension, allowing developers to introduce new behaviors, data structures, events, or messages that are specific to their program while remaining compatible with existing interfaces.

In graphical user interface programming, application-defined messages are a common mechanism for signaling events that are not part of the system message set. Operating systems such as Windows provide designated ranges of message identifiers to avoid collisions between system messages and user-defined messages. On Windows, messages in the range from WM_APP (0x8000) to 0xBFFF are intended for application-defined use within a single application, while WM_USER (0x0400) has historically been used by custom controls but can lead to conflicts when multiple components are combined. Developers typically define custom handlers and pass data through parameters, documenting the semantics so other components can respond appropriately.

In other ecosystems, application-defined extensions can take the form of user-defined events, plugin interfaces, or domain-specific data types. Design considerations include ensuring clear naming, versioning of interfaces, and avoiding hard dependencies that hinder reuse. Application-defined elements should be isolated from core system interfaces to minimize maintenance risks and promote portability.

See also: custom events, plugin architecture, API extension, user-defined types.