The difference between <tag></tag> and <tag/> is important if you're trying to write "polyglot" xml/html that can be parsed by either an xml parser or an html p

The difference between <tag></tag> and <tag/> is important if you're trying to write "polyglot" xml/html that can be parsed by either an xml parser or an html parser. For example <br></br> is not valid HTML, but a plain <br> is not valid XML. However <br/> works as either. On the other hand, an empty span has to be written <span></span>.