What does javascript: does in iframe src?

Question

   <iframe src="javascript:''" id="__gwt_historyFrame" tabIndex='-1' style="position:absolute;width:0;height:0;border:0"></iframe>

I would like to ask what did "javascript:" does in iframe src? I came across this code in a web application.

Basically, what i like about that is that they loaded body content via iframe -> like that google is doing. Does javascript: plays an important part?

E.g. http://www.webapplication.com/#Dashboard:142 Load content from dashboard.php / 142 is userid

E.g. http://www.webapplication.com/#settings:142 Load content from settings.php / 142 is userid

Answer 1

javascript:'' 

does absolutely nothing, it is used as a filler. Some use about:blank, or just an empty file, and this is another way.