Between frameworks like Ruby on Rails, Node.js, AngularJS and smaller libraries like Backbone.js, jQuery, and jQuery UI, I've relied more on code for all of them. Documentation has only ever helped me to get started, and as a quick reference. But do anything significant, and thorough understanding is simply a must; something I can only find in code.
I also do a good amount of work with the Twitter and Facebook APIs, and in my spare time work on a fairly complex Cocoa project. Working with all of these is a whole lot of poking at interfaces until they do what I want. These all have tons of documentation, but they'll never be pleasant for me to work with.
I use Django on the server side, the documentation is superb (compared to Angular's). I hardly ever need to dig inside the code, unless I want to do something quite special.
I have a good idea of how the framework works, what pieces fit together where, but I never feel the need to go in and read the code for it.
And what about proprietary software? I am sure there are plenty of frameworks where you can't get to look at the code.