Nested Context Language (NCL) is a declarative authoring language for hypermedia documents. NCL is a modular language, which provides several facilities for authoring a complete hypermedia document with synchronization relationships among its components. Among its main facilities, it treats hypermedia relations as first-class entities through the definition of hypermedia connectors, and it can specify arbitrary semantics for a hypermedia composition using the concept of composite templates. NCL modules can be added to standard web languages, such as XLink and SMIL.