Excuse me if this question is too elementary.

I don't know what the correct syntax is for HTML5 or if this even works the way I remember, but I was of the understanding that if the source file pointed to by the src attribute of the script tag was not found, the code between the tags is run instead. For instance:

<SCRIPT type="text/ecmascript" SRC="/script/jquery.js">
<--
alert(this.src + " was not included.");
-->
</SCRIPT>

If "/script/jquery.js" is not found this code will pop up an alert box that reads "jquery.js was not included". Is this understanding correct and does it apply to HTML5? Thanks.