Why is an element showing in Firebug is not showing in page source code?

Question

I am having a bizarre experience with Way2sms.com. When I log in and try to send a sms, there is this Send SMS button which I should click to do it. Now on checking this button out with Firebug, it shows a input element with a class of schButton. However this class is nowhere to be found in the source code of the page (though CTRL-U). Then I thought that may be the element is added through JS, hence it is not showing in source code. In that case, however, the class must be found in any script or external JS page which is included in the source code, but I again found none. How is it possible that an element of the page is present nowhere in the source code?

Answer 1

The javascript could be loaded dynamically - did you want the net tab of firebug and check all the scripts loaded there? It's not enough to look for the script listed in <SCRIPT> tags.

Also the class could be build dynamically. For example from the type of the input element plus the string 'sch'.