A decade ago, I embarked on designing a framework for creating interoperable component for creating educational webpages. See Virtual Apparatus Framework.
The key for co-operative interoperability is to enable the components to share data and hence can act on what other component is doing. The technology I have chosen 10 years ago is based on the Netscape's LiveConnect. Different vendors have different level of support of this and hence the VAF has been working and breaking continuously.
Today, I jumped on the idea of sharing via DOM. Here are the experiments:
page from http://www.ipa88.com and page from http://www.scormplayer.com. These pages are exactly the same. Please verify using view page source.
The page loads two scripts, one from www.ipa88.com and another from www.scormplayer.com. All scripts from ipa88.com are numbered oddly while those from scormplayer.com are numbered evenly.
Does this method post a security risk? I don't think so because the loading page has explicitly requested the loading of scripts from two domains - i.e. that's by design!
I have tested on windows XP with only Firefox and IE6. Please let me know your testing result on other platform/browser combination.