'''XL''' stands for eXtensible Language. It is a [[computer programming|computer]] [[programming language]] designed to support [[concept programming]].
XL features programmer-reconfigurable syntax and semantics. Compiler '''plug-ins''' can be used to add new features to the language. A base set of plug-ins offer a relatively standard [[imperative programming|imperative language]]. Programmers can write their own plug-ins to implement application-specific notations, such as [[derivative|symbolic differentiation]], which can then be used similarly to built-in language features.
