The world of XML is vast and growing, with a huge variety of standards and technologies that interact in complex ways. It can be difficult for beginners to navigate the most important aspects of XML, and for users to keep track of new entries and changes in the space. XML is a basic syntax upon which you develop local and global vocabularies. Previous in-depth articles have presented the most important standards relating to XML. This fourth article, provides a detailed cross-reference of all covered standards.