Many windows in Javascript need to refresh themselves to keep their information current. This option determines what method they should use to do this. Choosing 'javascript' means that each window will have a short JavaScript statement in with a timer to prompt the refresh. This is the most compatible method. Choosing 'http' means the refresh instruction is put in the HTTP header. This is a cleaner method but refreshes are interrupted or cancelled when a link in the window is clicked meaning that the window will no longer refresh and this would have to be done manually.