(4) the xml variant, <br/>, is based on changing NET to "/>", and
although any SGML document (and hence any HTML document before
HTML 5) can change the SGML declaration to allow />, the default
was <br/ and not <br/>
This wasn't altogether satisfactory because it meant you would be omitting the end-tag, so we actually amended SGML so that you could specify separate delimiters for start-tag close and the end-tag when using NET markup minimization. With this approach, the NESTC (net-enabling start-tag close) delimiter is "/", and the NET delimiter (used just for the end-tag) is ">". See
James
