From the opensource binary (qt-opensource-linux-x64-5.3.0-RC.run)
Open up Qt Creator and open up the help mode and click on the page:
qthelp://org.qt-project.qtdoc.530/qtdoc/qtmodules.html "All Modules"
The Qt WebKit link is missing. The installer package has a ./Docs/Qt-5.3/qtwebkit.qch file so Qt WebKit docs are built, but not when the other documentation is built.
Other links to Qt WebKit are either missing or pointing to the wrong section.
This may not be as critical as the qtwebkit.qch is in the package at least.