In addition to iFrames, you now also have a new item called Web Resources. This was necessary given that in the world of online you can limit yourself to custom pages hosted in the same web server in which CRM was running. As the web tools have expanded, so has Dynamics CRM.
In addition, Web Resources prevent you from having to copy and paste the same Jscript over and over again on various
Josh Beal sums it up in one really nice statement: “It is not a matter of can I do it...it is a matter of should I do it.” He also indicates that hacking away at some .JS files on a web server is a risky venture and potentially not upgradable.
There are now a number of Web Resources that developers can use ...