First, I had no idea that "/>" had a name. Solidus.

Second, the article is unclear on the "optional" nature of the solidus.

I'm pretty sure that the use of the solidus depends on whether you are using an HTML or XHTML serialization.

If you are sending the page as content-type text/html, you need to follow HTML format and leave out the solidus (that is, you follow the same rules as you would for HTML4).

If you are using the XHTML serialization you need to be using XML syntax and send the page as application/xml or application/xhtml+xml.