The thing with XHTML is many tags require to be closed that are not closed in HTML. An example is the <br> tag. In HTML it just looks like that, <br>. With XHTML on the other hand it must be closed. To close a tag like this add the / to the end. Now it looks like <br />. This is usually needed for codes without a </tag>. For example <div></div> does not require this.