Yes,I can't see the button about HTML5 feature ,either
the site had mentioned features as site description
Maybe it did not complete those convenient features,huh
Are you using Dreamweaver CS5, are you using The Extension Manager CS5, probably yes to all. (if not, then my soultion might not work!)
Because I've had the same problem as you, and I've found the solution myself as you can read in this post: http://forums.adobe.com/thread/647643?tstart=0, at least, in my case it worked. Let me tell you what you might wanna try in short so you do not need to read trough the entire thread!;
When you install the update into the "Extension Manager CS5", and all in there says it's enabled and all went well, but when you start "Dreamweaver CS5" and it didn't work... You need to do ONE more thing...
Now on the "Application Bar" (the bar which also let's you switch between certain layouts of dreamweaver itself), there are 3 icons, one for the "Layout", one for "Extend Dreamwaver" and one for "Site", what you just need to do is to open up "Extend Dreamweaver" and than choose "Extension Manager". It than pop's up the "Extension Manager CS5" itself, and if it's right (at least, in my case it was!), it jumps right into "Dreamweaver's CS5" own extension folder, and in there you problably see that the extension is disabled... You just have to turn it on in there aswell, restart Dreamweaver, and voila, you now see the "Multiscreen" Document-toolbar-button and in all other places it is mentioned.
Hope this also works for you if you''ve got the Extension Manager!
Post back if it worked for you or not!
Works for me!!!
THANK YOU!!! Its been 2 days of trying to find the solution... I even reinstalled the whole CS... hahahaha