You can look at the source code of any extension, doesn't have to be released under OSI-compliant license. <Chrome Profile Folder>/Extensions/<extension code>.

Get the Chrome profile folder for your platform from: http://www.chromium.org/user-experience/user-data-directory (note, may not be "Default" if you use a created user profile.)

Get the extension number from chrome://extensions/

One thing that needs to be taken care of is updates-gone-rogue (a la HoverZoom, for example.)