Inline Documentation

In general, I think it would be helpful to have mouseover tooltips, or a [?] box that opens up with more info, or a link to a website with more info about each of the metatags and http header options. The help text that is currently listed is not completely useful, like, "The HandheldFriendly meta-tag was used initially by older Palm and Blackberry models as well as browsers like AvantGo."
A better description might be: "Enabling this option prevents the BlackBerry Browser from scaling the content in page view."

Also it might be a good idea to include the warning about the IE Edge mode, as the Microsoft website states, "Because edge mode documents display webpages using the highest mode available to the version of Internet Explorer used to view them, it is recommended that you should only use this document mode for testing purposes only. Do not use it for production uses."
http://msdn.microsoft.com/en-us/library/cc288325(v=vs.85).aspx

BTW the 4.x version is slick, nice job! And I'm happy to help contribute to documentation, I'm just noting some of my thoughts & findings here for the time being.