Starting from version 7 Vim supports context aware completion of XML files (and others). In particular, when the file being edited is an XML file, completion can be driven by the grammar extracted from a Document Type Definition (DTD).

For this feature to work the user should put an XML data file corresponding to the desired DTD in a autoload/xml directory contained in a directory belonging to Vim's 'runtimepath' (for example ~/.vim/autoload/xml/).

dtd2vim is the program that creates XML data files from DTDs. Given as input a DTD file.dtd it will create a file.vim XML data file. dialectname will be part of dictionary name and will be used as argument for the :XMLns command.