An XML editor is a software program used to author, edit, or otherwise manipulate XML documents. Some tools are non-validating editors, which means that while they do check for the well-formedness of an XML document (all XML tools must do this!) they do not interpret a potential Document Type Definition (DTD) to validate the XML document against the rules described in the DTD. Others are validating editors and support DTD-based validation of XML documents, which is required for all publishing or data exchange applications.