In information technology, extensible describes something, such as a program, programming language, or protocol, that is designed so that users or developers can expand or add to its capabilities. Extensibility can be a primary reason for the system, as in the case of the Extensible Markup Language (XML), or it may be only a minor feature.

Approaches to extensibility include facilities (sometimes called hooks) for allowing users to insert their own program routines, the ability to define new data types, and the ability to define new formatting markup tags.

This was last updated in March 2007

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