Every browser that supports XHTML (Firefox, Opera, Safari, IE9) supports self-closing syntax on every element.
<div/>, <script/>, <br></br> all should work just fine. If they don't, then you have HTML with inappropriately added XHTML DOCTYPE.
DOCTYPE does not change how document is interpreted. Only MIME type does.
W3C decision about ignoring DOCTYPE:
The HTML WG has discussed this issue: the intention was to allow old
(HTML-only) browsers to accept XHTML 1.0 documents by following the
guidelines, and serving them as text/html. Therefore, documents served as
text/html should be treated as HTML and not as XHTML.
It's a very common pitfall, because W3C Validator largely ignores that rule, but browsers follow it religiously. Read
Understanding HTML, XML and XHTML from WebKit blog:
In fact, the vast majority of supposedly XHTML documents on the internet are served as text/html. Which means they are not XHTML at all, but actually invalid HTML that’s getting by on the error handling of HTML parsers. All those “Valid XHTML 1.0!” links on the web are really saying “Invalid HTML 4.01!”.
To test whether you have real XHTML or invalid HTML with XHTML's DOCTYPE, put this in your document:
<span style="color:green"><span style="color:red"/>
If it's red, it's HTML. Green is XHTML.
</span>
It validates, and in real XHTML it works perfectly (see: 1 vs 2). If you can't believe your eyes (or don't know how to set MIME types), open your page via XHTML proxy.
Another way to check is view source in Firefox. It will highlight slashes in red when they're invalid.
In HTML5/XHTML5 this hasn't changed, and the distinction is even clearer, because you don't even have additional DOCTYPE. Content-Type is the king.
For the record, the XHTML spec allows any element to be self-closing by making XHTML an XML application: [emphasis mine]
Empty-element tags may be used for any element which has no content, whether or not it is declared using the keyword EMPTY.
It's also explicitly shown in the XHTML spec:
Empty elements must either have an end tag or the start tag must end with />. For instance, <br/> or <hr></hr>
Some web frameworks (e.g. Ruby on Rails) get around that by including a hidden _method parameter in the form with the value of the "actual" method, e.g.:
<form action="/posts/xxxxx" method="POST">
<input type="hidden" name="_method" value="DELETE">
<input type="submit" value="delete">
</form>
The framework then rewrites the request on the server side before processing to use the value of the _method parameter as the HTTP method.
Don't know if this helps you.
Best Answer
No. The HTML 5 spec mentions:
I.e. HTML forms only support GET and POST as HTTP request methods. A workaround for this is to tunnel other methods through POST by using a hidden form field which is read by the server and the request dispatched accordingly.
However, GET, POST, PUT and DELETE are supported by the implementations of XMLHttpRequest (i.e. AJAX calls) in all the major web browsers (IE, Firefox, Safari, Chrome, Opera).