XPontus

XPontus XML Editor is a multiplatform open-source text editor for the XML programming language, which is extensible using plugins and has support for XPath 1.0 and 2.0. You can use XPontus XML Editor to validate DTDs, XML schemas (individual and batch), and Relax NG, as well as to perform XSL transformations to these formats: HTML, XML, PDF, and SVG. XPontus XML Editor includes the following features as a text editor: code completion and indentation, syntax highlighting, document structure explorer, and more.