XSL is the Extensible Stylesheet Language that can be used to transform XML formats to other formats (XSLT) or to format XML-documents (XSLFO) for viewing, analogous to CSS (Cascading Style Sheets).
A language to address and have access to the XML hierarchy, elements and attributes. Supports XSL and XPointer.
A extended linking language, much more powerful than todays linking within HTML.
A language that allows definition of valid data-fields and types, as well as rules for validating XML files. Much more powerful than DTD's (Document Type Definitions)
A query language analogous to SQL.
SVG (Scalable Vector Graphics) is a Vector-Graphics Language that can transport all Graphics that typical Vector Drawing Packages like Adobe Illustrator or CorelDraw can produce. Because it is well-documented and simple it is also possible to create and edit them with simple text or XML-Editors or scripting languages. It is in particular powerful for creating interactive Maps on the Web. Animations are simple by using a SMIL (Synchronized Multimedia Language) Syntax. SVG could be used as a viewing component, translated from CaveXML, that is outputted from cave-surveying-software with adjusted coordinates.
Extensible 3D language. XML successor of VRML. Highly interactive through interpolators, sensors, etc.
Synchronized Multimedia Language. Allows integration of different Multimedia elements in a time-line based approach. Allows Animations.